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Decision-making involves the use of both automatic and controlled processes, but also depends on the person and situation, and given a person's experiences and current situation the decision process may differ. Given that there are two decision processes with differing goals one is more likely to be more useful in particular situations. For example, a person is presented with a decision involving a selfish but rational motive and a social motive. Depending on the individual one of the motives will be more appealing than the other, but depending on the situation the preference for one motive or the other may change.
Using the dual-process theory it is important to consider whether one motive is more automatic than the other, and in this particular case the automaticity would depend on the individual and their experiences. A selfish person may choose the selfish motive with more automaticity than a non-selfish person, and yet a controlled process may still outweigh this based on external factors such as the situation, monetary gains, or societal pressure. Although there is likely to be a stable preference for which motive one will select based on the individual it is important to remember that external factors will influence the decision.
Dual process theory also provides a different source of behavioral heterogeneity in economics. It is mostly assumed within economics that this heterogeneity comes from differences in taste and rationality, while dual process theory indicates necessary considerations of which processes are automated and how these different processes may interact within decision making. Evidence Belief bias effect A belief bias is the tendency to judge the strength of arguments based on the plausibility of their conclusion rather than how strongly they support that conclusion. Some evidence suggests that this bias results from competition between logical (System 2) and belief-based (System 1) processes during evaluation of arguments.
Studies on belief-bias effect were first designed by Jonathan Evans to create a conflict between logical reasoning and prior knowledge about the truth of conclusions. Participants are asked to evaluate syllogisms that are: valid arguments with believable conclusions, valid arguments with unbelievable conclusions, invalid arguments with believable conclusions, and invalid arguments with unbelievable conclusions. Participants are told to only agree with conclusions that logically follow from the premises given. The results suggest when the conclusion is believable, people erroneously accept invalid conclusions as valid more often than invalid arguments are accepted which support unpalatable conclusions. This is taken to suggest that System 1 beliefs are interfering with the logic of System 2.
Tests with working memory De Neys conducted a study that manipulated working memory capacity while answering syllogistic problems. This was done by burdening executive processes with secondary tasks. Results showed that when System 1 triggered the correct response, the distractor task had no effect on the production of a correct answer which supports the fact that System 1 is automatic and works independently of working memory, but when belief-bias was present (System 1 belief-based response was different from the logically correct System 2 response) the participants performance was impeded by the decreased availability of working memory. This falls in accordance with the knowledge about System 1 and System 2 of the dual-process accounts of reasoning because System 1 was shown to work independent of working memory, and System 2 was impeded due to a lack of working memory space so System 1 took over which resulted in a belief-bias.
fMRI studies Vinod Goel and others produced neuropsychological evidence for dual-process accounts of reasoning using fMRI studies. They provided evidence that anatomically distinct parts of the brain were responsible for the two different kinds of reasoning. They found that content-based reasoning caused left temporal hemisphere activation whereas abstract formal problem reasoning activated the parietal system. They concluded that different kinds of reasoning, depending on the semantic content, activated one of two different systems in the brain. A similar study incorporated fMRI during a belief-bias test. They found that different mental processes were competing for control of the response to the problems given in the belief-bias test.
The prefrontal cortex was critical in detecting and resolving conflicts, which are characteristic of System 2, and had already been associated with that System 2. The ventral medial prefrontal cortex, known to be associated with the more intuitive or heuristic responses of System 1, was the area in competition with the prefrontal cortex. Near-infrared spectroscopy Tsujii and Watanabe did a follow-up study to Goel and Dolan's fMRI experiment. They examined the neural correlates on the inferior frontal cortex (IFC) activity in belief-bias reasoning using near-infrared spectroscopy (NIRS). Subjects performed a syllogistic reasoning task, using congruent and incongruent syllogisms, while attending to an attention-demanding secondary task.
The interest of the researchers was in how the secondary-tasks changed the activity of the IFC during congruent and incongruent reasoning processes. The results showed that the participants performed better in the congruent test than in the incongruent test (evidence for belief bias); the high demand secondary test impaired the incongruent reasoning more than it impaired the congruent reasoning. NIRS results showed that the right IFC was activated more during incongruent trials. Participants with enhanced right IFC activity performed better on the incongruent reasoning than those with decreased right IFC activity. This study provided some evidence to enhance the fMRI results that the right IFC, specifically, is critical in resolving conflicting reasoning, but that it is also attention-demanding; its effectiveness decreases with loss of attention.
The loss of effectiveness in System 2 following loss of attention makes the automatic heuristic System 1 take over, which results in belief bias. Matching bias Matching bias is a non-logical heuristic. The matching bias is described as a tendency to use lexical content matching of the statement about which one is reasoning, to be seen as relevant information and do the opposite as well, ignore relevant information that doesn't match. It mostly affects problems with abstract content. It doesn't involve prior knowledge and beliefs but it is still seen as a System 1 heuristic that competes with the logical System 2.
The Wason selection task provides evidence for the matching bias. The test is designed as a measure of a person's logical thinking ability. Performance on the Wason Selection Task is sensitive to the content and context with which it is presented. If you introduce a negative component into the conditional statement of the Wason Selection Task, e.g. 'If there is an A one side of the card then there is not a 3 on the other side', there is a strong tendency to choose cards that match the items in the negative condition to test, regardless of their logical status.
Changing the test to be a test of following rules rather than truth and falsity is another condition where the participants will ignore the logic because they will simply follow the rule, e.g. changing the test to be a test of a police officer looking for underaged drinkers. The original task is more difficult because it requires explicit and abstract logical thought from System 2, and the police officer test is cued by relevant prior knowledge from System 1. Studies have shown that you can train people to inhibit matching bias which provides neuropsychological evidence for the dual-process theory of reasoning.
When you compare trials before and after the training there is evidence for a forward shift in activated brain area. Pre-test results showed activation in locations along the ventral pathway and post-test results showed activation around the ventro-medial prefrontal cortex and anterior cingulate. Matching bias has also been shown to generalise to syllogistic reasoning. Evolution Dual-process theorists claim that System 2, a general purpose reasoning system, evolved late and worked alongside the older autonomous sub-systems of System 1. The success of Homo sapiens lends evidence to their higher cognitive abilities above other hominids. Mithen theorizes that the increase in cognitive ability occurred 50,000 years ago when representational art, imagery, and the design of tools and artefacts are first documented.
She hypothesizes that this change was due to the adaptation of System 2. Most evolutionary psychologists do not agree with dual-process theorists. They claim that the mind is modular, and domain-specific, thus they disagree with the theory of the general reasoning ability of System 2. They have difficulty agreeing that there are two distinct ways of reasoning and that one is evolutionarily old, and the other is new. To ease this discomfort, the theory is that once System 2 evolved, it became a 'long leash' system without much genetic control which allowed humans to pursue their individual goals. Issues with the dual-process account of reasoning The dual-process account of reasoning is an old theory, as noted above.
But according to Evans it has adapted itself from the old, logicist paradigm, to the new theories that apply to other kinds of reasoning as well. And the theory seems more influential now than in the past which is questionable. Evans outlined 5 "fallacies": All dual-process theories are essentially the same. There is a tendency to assume all theories that propose two modes or styles of thinking are related and so they end up all lumped under the umbrella term of "dual-process theories". There are just two systems underlying System 1 and System 2 processing. There are clearly more than just two cognitive systems underlying people's performance on dual-processing tasks.
Hence the change to theorizing that processing is done in two minds that have different evolutionary histories and that each have multiple sub-systems. System 1 processes are responsible for cognitive biases; System 2 processes are responsible for normatively correct responding. Both System 1 and System 2 processing can lead to normative answers and both can involve cognitive biases. System 1 processing is contextualised while System 2 processing is abstract. Recent research has found that beliefs and context can influence System 2 processing as well as System 1. Fast processing indicates the use of System 1 rather than System 2 processes.
Just because a processing is fast does not mean it is done by System 1. Experience and different heuristics can influence System 2 processing to go faster. Another argument against dual-process accounts for reasoning which was outlined by Osman is that the proposed dichotomy of System 1 and System 2 does not adequately accommodate the range of processes accomplished. Moshman proposed that there should be four possible types of processing as opposed to two. They would be implicit heuristic processing, implicit rule-based processing, explicit heuristic processing, and explicit rule-based processing. Another fine-grained division is as follows: implicit action-centered processes, implicit non-action-centered processes, explicit action-centered processes, and explicit non-action-centered processes (that is, a four-way division reflecting both the implicit-explicit distinction and the procedural-declarative distinction).
In response to the question as to whether there are dichotomous processing types, many have instead proposed a single-system framework which incorporates a continuum between implicit and explicit processes. Alternative model The dynamic graded continuum (DGC), originally proposed by Cleeremans and Jiménez is an alternative single system framework to the dual-process account of reasoning. It has not been accepted as better than the dual-process theory; it is instead usually used as a comparison with which one can evaluate the dual-process model. The DGC proposes that differences in representation generate variation in forms of reasoning without assuming a multiple system framework.
It describes how graded properties of the representations that are generated while reasoning result in the different types of reasoning. It separates terms like implicit and automatic processing where the dual-process model uses the terms interchangeably to refer to the whole of System 1. Instead the DGC uses a continuum of reasoning that moves from implicit, to explicit, to automatic. Fuzzy-trace theory According to Charles Brainerd and Valerie Reyna's fuzzy-trace theory of memory and reasoning, people have two memory representations: verbatim and gist. Verbatim is memory for surface information (e.g. the words in this sentence) whereas gist is memory for semantic information (e.g.
the meaning of this sentence). This dual process theory posits that we encode, store, retrieve, and forget the information in these two traces of memory separately and completely independently of each other. Furthermore, the two memory traces decay at different rates: verbatim decays quickly, while gist lasts longer. In terms of reasoning, fuzzy-trace theory posits that as we mature, we increasingly rely more on gist information over verbatim information. Evidence for this lies in framing experiments where framing effects become stronger when verbatim information (percentages) are replaced with gist descriptions. Other experiments rule out predictions of prospect theory (extended and original) as well as other current theories of judgment and decision making.
See also References External links Laboratory for Rational Decision Making Category:Cognition Category:Cognitive psychology
The Indus River (also called the Sindhū) is one of the longest rivers in Asia. It flows through China (western Tibet), India (Jammu and Kashmir) and Pakistan. Originating in the Tibetan Plateau in the vicinity of Lake Manasarovar, the river runs a course through the Ladakh region of Jammu and Kashmir, towards Gilgit and Baltistan and then flows in a southerly direction along the entire length of Pakistan to merge into the Arabian Sea near the port city of Karachi in Sindh. It is the longest river of Pakistan. The river has a total drainage area exceeding . Its estimated annual flow stands at around , twice that of the Nile River and three times that of the Tigris and Euphrates rivers combined, making it one of the largest rivers in the world in terms of annual flow.
The Zanskar is its left bank tributary in Ladakh. In the plains, its left bank tributary is the Panjnad which itself has five major tributaries, namely, the Chenab, Jhelum, the Ravi, the Beas, and the Sutlej. Its principal right bank tributaries are the Shyok, the Gilgit, the Kabul, the Gomal, and the Kurram. Beginning in a mountain spring and fed with glaciers and rivers in the Himalayan, Karakoram and Hindu Kush ranges, the river supports ecosystems of temperate forests, plains and arid countryside. The northern part of the Indus Valley, with its tributaries, forms the Punjab region, while the lower course of the river is known as Sindh and ends in a large delta.
The river has historically been important to many cultures of the region. The 3rd millennium BC saw the rise of a major urban civilization of the Bronze Age. During the 2nd millennium BC, the Punjab region was mentioned in the hymns of the Hindu Rigveda as Sapta Sindhu and the Zoroastrian Avesta as Hapta Hindu (both terms meaning "seven rivers"). Early historical kingdoms that arose in the Indus Valley include Gandhāra, and the Ror dynasty of Sauvīra. The Indus River came into the knowledge of the West early in the Classical Period, when King Darius of Persia sent his Greek subject Scylax of Caryanda to explore the river, c. 515 BC.
Etymology and names This river was known to the ancient Indians in Sanskrit as Sindhu and the Persians as Hindu which was regarded by both of them as "the border river". The variation between the two names is explained by the Old Iranian sound change *s > h, which occurred between 850–600 BCE according to Asko Parpola. From the Persian Achaemenid Empire, the name passed to the Greeks as Indós (Ἰνδός). It was adopted by the Romans as Indus. The meaning of Sindhu as a "large body of water, sea, or ocean" is a later meaning in Classical Sanskrit. A later Persian name for the river was Darya, which similarly has the connotations of large body of water and sea.
Other variants of the name Sindhu include Assyrian Sinda (as early as the 7th century BC), Persian Ab-e-sind, Pashto Abasind, Arab Al-Sind, Chinese Sintow, and Javanese Santri. In other languages of the region, the river is known as सिन्धु (Sindhu) in Hindi, سنڌو (Sindhu) in Sindhi, (Sindh) in Shahmukhi Punjabi, ਸਿੰਧ ਨਦੀ (Sindh Nadī) in Gurmukhī Punjabi, اباسين (Abāsin lit. "Father of Rivers") in Pashto, نهر السند (Nahar al-Sind) in Arabic, སེང་གེ་གཙང་པོ། (singi khamban lit. "Lion River" or Lion Spring) in Tibetan, (Yìndù) in Chinese, Nilab in Turki and සින්දු නදී (Sindhu Nadi) in Sinhalese. Description The Indus River provides key water resources for Pakistan's economy – especially the breadbasket of Punjab province, which accounts for most of the nation's agricultural production, and Sindh.
The word Punjab means "land of five rivers" and the five rivers are Jhelum, Chenab, Ravi, Beas and Sutlej, all of which finally flow into the Indus. The Indus also supports many heavy industries and provides the main supply of potable water in Pakistan. The ultimate source of the Indus is in Tibet; the river begins at the confluence of the Sengge Zangbo and Gar Tsangpo rivers that drain the Nganglong Kangri and Gangdise Shan (Gang Rinpoche, Mt. Kailash) mountain ranges. The Indus then flows northwest through Ladakh, India, and Baltistan into Gilgit, just south of the Karakoram range. The Shyok, Shigar and Gilgit rivers carry glacial waters into the main river.
It gradually bends to the south and descends into the Punjab plains at Kalabagh, Pakistan. The Indus passes gigantic gorges deep near the Nanga Parbat massif. It flows swiftly across Hazara and is dammed at the Tarbela Reservoir. The Kabul River joins it near Attock. The remainder of its route to the sea is in the plains of the Punjab and Sindh, where the flow of the river becomes slow and highly braided. It is joined by the Panjnad at Mithankot. Beyond this confluence, the river, at one time, was named the Satnad River (sat = "seven", nadī = "river"), as the river now carried the waters of the Kabul River, the Indus River and the five Punjab rivers.
Passing by Jamshoro, it ends in a large delta to the South of Thatta in the Sindh province of Pakistan The Indus is one of the few rivers in the world to exhibit a tidal bore. The Indus system is largely fed by the snows and glaciers of the Himalayas, Karakoram and the Hindu Kush ranges of Tibet, the Indian states and union territories of Jammu and Kashmir, Ladakh and Himachal Pradesh and Gilgit-Baltistan region of Pakistan. The flow of the river is also determined by the seasons – it diminishes greatly in the winter, while flooding its banks in the monsoon months from July to September.
There is also evidence of a steady shift in the course of the river since prehistoric times – it deviated westwards from flowing into the Rann of Kutch and adjoining Banni grasslands after the 1816 earthquake. Presently, Indus water flows in to the Rann of Kutch during its floods breaching flood banks. The traditional source of the river is the Senge Khabab or "Lion's Mouth", a perennial spring, not far from the sacred Mount Kailash marked by a long low line of Tibetan chortens. There are several other tributaries nearby, which may possibly form a longer stream than Senge Khabab, but unlike the Senge Khabab, are all dependent on snowmelt.
The Zanskar River, which flows into the Indus in Ladakh, has a greater volume of water than the Indus itself before that point. History The major cities of the Indus Valley Civilisation, such as Harappa and Mohenjo-daro, date back to around 3300 BC, and represent some of the largest human habitations of the ancient world. The Indus Valley Civilisation extended from across northeast Afghanistan to Pakistan and northwest India, with an upward reach from east of Jhelum River to Ropar on the upper Sutlej. The coastal settlements extended from Sutkagan Dor at the Pakistan, Iran border to Kutch in modern Gujarat, India.
There is an Indus site on the Amu Darya at Shortughai in northern Afghanistan, and the Indus site Alamgirpur at the Hindon River is located only from Delhi. To date, over 1,052 cities and settlements have been found, mainly in the general region of the Ghaggar-Hakra River and its tributaries. Among the settlements were the major urban centres of Harappa and Mohenjo-daro, as well as Lothal, Dholavira, Ganeriwala, and Rakhigarhi. Only 90–96 of more than 800 known Indus Valley sites have been discovered on the Indus and its tributaries. The Sutlej, now a tributary of the Indus, in Harappan times flowed into the Ghaggar-Hakra River, in the watershed of which were more Harappan sites than along the Indus.
Most scholars believe that settlements of Gandhara grave culture of the early Indo-Aryans flourished in Gandhara from 1700 BC to 600 BC, when Mohenjo-daro and Harappa had already been abandoned. The Rigveda describes several rivers, including one named "Sindhu". The Rigvedic "Sindhu" is thought to be the present-day Indus river. It is attested 176 times in its text, 94 times in the plural, and most often used in the generic sense of "river". In the Rigveda, notably in the later hymns, the meaning of the word is narrowed to refer to the Indus river in particular, e.g. in the list of rivers mentioned in the hymn of Nadistuti sukta.
The Rigvedic hymns apply a feminine gender to all the rivers mentioned therein, except for the Brahmaputra. The word "India" is derived from the Indus River. In ancient times, "India" initially referred to those regions immediately along the east bank of the Indus, but by 300 BC, Greek writers including Herodotus and Megasthenes were applying the term to the entire subcontinent that extends much farther eastward. The lower basin of the Indus forms a natural boundary between the Iranian Plateau and the Indian subcontinent; this region embraces all or parts of the Pakistani provinces Balochistan, Khyber Pakhtunkhwa, Punjab and Sindh and the countries Afghanistan and India.
The first West Eurasian empire to annex the Indus Valley was the Persian Empire, during the reign of Darius the Great. During his reign, the Greek explorer Scylax of Caryanda was commissioned to explore the course of the Indus. It was crossed by the invading armies of Alexander, but after his Macedonians conquered the west bank—joining it to the Hellenic world, they elected to retreat along the southern course of the river, ending Alexander's Asian campaign. Alexander's admiral Nearchus set out from the Indus Delta to explore the Persian Gulf, until reaching the Tigris River. The Indus Valley were later dominated by the Mauryan and Kushan Empires, Indo-Greek Kingdoms, Indo-Scythians and Hepthalites.
Over several centuries Muslim armies of Muhammad bin Qasim, Mahmud of Ghazni, Mohammed Ghori, Tamerlane and Babur crossed the river to invade Sindh and Punjab, providing a gateway to the Indian subcontinent. Geography Tributaries Beas River Chenab River Gar River Gilgit River Gomal River Hunza River Jhelum River Kabul River Kunar River Kurram River Panjnad River Ravi River Shyok River Soan River Suru River Satluj River Swat River Zanskar River Zhob River Geology The Indus river feeds the Indus submarine fan, which is the second largest sediment body on the Earth. It consists of around 5 million cubic kilometres of material eroded from the mountains.
Studies of the sediment in the modern river indicate that the Karakoram Mountains in northern Pakistan and India are the single most important source of material, with the Himalayas providing the next largest contribution, mostly via the large rivers of the Punjab (Jhelum, Ravi, Chenab, Beas and Sutlej). Analysis of sediments from the Arabian Sea has demonstrated that prior to five million years ago the Indus was not connected to these Punjab rivers which instead flowed east into the Ganga and were captured after that time. Earlier work showed that sand and silt from western Tibet was reaching the Arabian Sea by 45 million years ago, implying the existence of an ancient Indus River by that time.
The delta of this proto-Indus river has subsequently been found in the Katawaz Basin, on the Afghan-Pakistan border. In the Nanga Parbat region, the massive amounts of erosion due to the Indus river following the capture and rerouting through that area is thought to bring middle and lower crustal rocks to the surface. In November 2011, satellite images showed that the Indus river had re-entered India, feeding Great Rann of Kutch, Little Rann of Kutch and a lake near Ahmedabad known as Nal Sarovar. Heavy rains had left the river basin along with the Lake Manchar, Lake Hemal and Kalri Lake (all in modern-day Pakistan) inundated.
This happened two centuries after the Indus river shifted its course westwards following the 1819 Rann of Kutch earthquake. The Induan Age at start of the Triassic Period of geological time is named for the Indus region. Wildlife Accounts of the Indus valley from the times of Alexander's campaign indicate a healthy forest cover in the region, which has now considerably receded. The Mughal Emperor Babur writes of encountering rhinoceroses along its bank in his memoirs (the Baburnama). Extensive deforestation and human interference in the ecology of the Shivalik Hills has led to a marked deterioration in vegetation and growing conditions.
The Indus valley regions are arid with poor vegetation. Agriculture is sustained largely due to irrigation works. The Indus river and its watershed has a rich biodiversity. It is home to around 25 amphibian species. Mammals The Indus river dolphin (Platanista indicus minor) is found only in the Indus River. It is subspecies of the South Asian river dolphin. The Indus river dolphin formerly also occurred in the tributaries of the Indus river. According to the World Wildlife Fund it is one of the most threatened cetaceans with only about 1,000 still existing. There are two otter species in the Indus River basin: the Eurasian otter in the northeastern highland sections and the smooth-coated otter elsewhere in the river basin.
The smooth-coated otters in the Indus River represent a subspecies found nowhere else, the Sindh otter (Lutrogale perspicillata sindica). Fish The Indus River basin has a high diversity, being the home of more than 180 freshwater fish species, including 22 which are found nowhere else. Fish also played a major role in earlier cultures of the region, including the ancient Indus Valley Civilisation where depictions of fish were frequent. The Indus script has a commonly used fish sign, which in its various forms may simply have meant "fish", or referred to stars or gods. In the uppermost, highest part of the Indus River basin there are relatively few genera and species: Diptychus, Ptychobarbus, Schizopyge, Schizopygopsis and Schizothorax snowtrout, Triplophysa loaches, and the catfish Glyptosternon reticulatum.
Going downstream these are soon joined by the golden mahseer Tor putitora (alternatively T. macrolepis, although it often is regarded as a synonym of T. putitora) and Schistura loaches. Downriver from around Thakot, Tarbela, the Kabul–Indus river confluence, Attock Khurd and Peshawar the diversity rises strongly, including many cyprinids (Amblypharyngodon, Aspidoparia, Barilius, Chela, Cirrhinus, Crossocheilus, Cyprinion, Danio, Devario, Esomus, Garra, Labeo, Naziritor, Osteobrama, Pethia, Puntius, Rasbora, Salmophasia, Securicula and Systomus), true loaches (Botia and Lepidocephalus), stone loaches (Acanthocobitis and Nemacheilus), ailiid catfish (Clupisoma), bagridae catfish (Batasio, Mystus, Rita and Sperata), airsac catfish (Heteropneustes), schilbid catfish (Eutropiichthys), silurid catfish (Ompok and Wallago), sisorid catfish (Bagarius, Gagata, Glyptothorax and Sisor), gouramis (Trichogaster), nandid leaffish (Nandus), snakeheads (Channa), spiny eel (Macrognathus and Mastacembelus), knifefish (Notopterus), glassfish (Chanda and Parambassis), clupeids (Gudusia), needlefish (Xenentodon) and gobies (Glossogobius), as well as a few introduced species.
As the altitude further declines the Indus basin becomes overall quite slow-flowing as it passes through the Punjab Plain. Major carp become common, and chameleonfish (Badis), mullet (Sicamugil) and swamp eel (Monopterus) appear. In some upland lakes and tributaries of the Punjab region snowtrout and mahseer are still common, but once the Indus basin reaches its lower plain the former group is entirely absent and the latter are rare. Many of the species of the middle sections of the Indus basin are also present in the lower. Notable examples of genera that are present in the lower plain but generally not elsewhere in the Indus River basin are the Aphanius pupfish, Aplocheilus killifish, palla fish (Tenualosa ilisha), catla (Labeo catla), rohu (Labeo rohita) and Cirrhinus mrigala.
The lowermost part of the river and its delta are home to freshwater fish, but also a number of brackish and marine species. This includes including pomfret and prawns. The large delta has been recognized by conservationists as an important ecological region. Here, the river turns into many marshes, streams and creeks and meets the sea at shallow levels. Palla fish (Tenualosa ilisha) of the river is a delicacy for people living along the river. The population of fish in the river is moderately high, with Sukkur, Thatta, and Kotri being the major fishing centres – all in the lower Sindh course.
As a result, damming and irrigation has made fish farming an important economic activity. Economy The Indus is the most important supplier of water resources to the Punjab and Sindh plains – it forms the backbone of agriculture and food production in Pakistan. The river is especially critical since rainfall is meagre in the lower Indus valley. Irrigation canals were first built by the people of the Indus Valley Civilisation, and later by the engineers of the Kushan Empire and the Mughal Empire. Modern irrigation was introduced by the British East India Company in 1850 – the construction of modern canals accompanied with the restoration of old canals.
The British supervised the construction of one of the most complex irrigation networks in the world. The Guddu Barrage is long – irrigating Sukkur, Jacobabad, Larkana and Kalat. The Sukkur Barrage serves over . After Pakistan came into existence, a water control treaty signed between India and Pakistan in 1960 guaranteed that Pakistan would receive water from the Indus River and its two tributaries the Jhelum River & the Chenab River independently of upstream control by India. The Indus Basin Project consisted primarily of the construction of two main dams, the Mangla Dam built on the Jhelum River and the Tarbela Dam constructed on the Indus River, together with their subsidiary dams.
The Pakistan Water and Power Development Authority undertook the construction of the Chashma-Jhelum link canal – linking the waters of the Indus and Jhelum rivers – extending water supplies to the regions of Bahawalpur and Multan. Pakistan constructed the Tarbela Dam near Rawalpindi – standing long and high, with an long reservoir. It supports the Chashma Barrage near Dera Ismail Khan for irrigation use and flood control and the Taunsa Barrage near Dera Ghazi Khan which also produces 100,000 kilowatts of electricity. The Kotri Barrage near Hyderabad is long and provides additional water supplies for Karachi. The extensive linking of tributaries with the Indus has helped spread water resources to the valley of Peshawar, in the Khyber Pakhtunkhwa.
The extensive irrigation and dam projects provide the basis for Pakistan's large production of crops such as cotton, sugarcane and wheat. The dams also generate electricity for heavy industries and urban centers. People The inhabitants of the regions are mainly Muslim as Pakistan is an Islamic country through which the Indus river passes and forms a major natural feature and resource are diverse in ethnicity, religion, national and linguistic backgrounds. On the northern course of the river in the union territory of Ladakh in India, live the Buddhist people of Ladakh, of Tibetan stock, and the Dards of Indo-Aryan or Dardic stock and practising Islam.
Then it descends into Baltistan, northern Pakistan passing the main Balti city of Skardu. A river from Dubair Bala also drains into it at Dubair Bazar. People living in this area are mainly Kohistani and speak the Kohistani language. Major areas through which the Indus river passes in Kohistan are Dasu, Pattan and Dubair. As it continues through Pakistan, the Indus river forms a distinctive boundary of ethnicity and cultures – upon the western banks the population is largely Pashtun, Baloch, and of other Iranian stock. The eastern banks are largely populated by people of Indo-Aryan stock, such as the Punjabis and the Sindhis.
In northern Punjab and the Khyber Pakhtunkhwa, ethnic Pashtun tribes live alongside Dardic people in the hills (Khowar, Kalash, Shina, etc. ), Burushos (in Hunza), and Punjabi people. The people living along the Indus river speak Punjabi and Sindhi on the eastern side (in Punjab and Sindh provinces respectively), Pushto plus Balochi as well as Barohi (in Khyber Pakhtoonkha and Baluchistan provinces). In the province of Sindh, the upper third of the river is inhabited by people speaking Saraiki; which is a somewhat transitional dialect of the Punjabi and Sindhi languages. The ethnicities of the Indus Valley (Pakistan and Northwest India) have a greater amount of ANI (or West Eurasian) admixture than other South Asians, including inputs from Western Steppe Herders, with evidence of more sustained and multi-layered migrations from the west.
Modern issues The Indus is a strategically vital resource for Pakistan's economy and society. After Pakistan and India declared Independence from the British Raj, the use of the waters of the Indus and its five eastern tributaries became a major dispute between India and Pakistan. The irrigation canals of the Sutlej valley and the Bari Doab were split – with the canals lying primarily in Pakistan and the headwork dams in India disrupting supply in some parts of Pakistan. The concern over India building large dams over various Punjab rivers that could undercut the supply flowing to Pakistan, as well as the possibility that India could divert rivers in the time of war, caused political consternation in Pakistan.
Holding diplomatic talks brokered by the World Bank, India and Pakistan signed the Indus Waters Treaty in 1960. The treaty gave India control of the three easternmost rivers of the Punjab, the Sutlej, the Beas and the Ravi, while Pakistan gained control of the three western rivers, the Jhelum, the Chenab and the Indus. India retained the right to use of the western rivers for non-irrigation projects. Large-scale diversion of the river's water for irrigation has raised far-reaching issues. Sediment clogging from poor maintenance of canals has affected agricultural production and vegetation on numerous occasions. Irrigation itself is increasing soil salinization, reducing crop yields and in some cases rendering farmland useless for cultivation.
And ecologically, the reduced flow of fresh water and silt into the Indus delta is threatening the area's mangrove forests. There are also concerns that the Indus River may be shifting its course westwards, although the progression spans centuries. Indus delta Originally, the delta used to receive almost all of the water from the Indus river, which has an annual flow of approximately , and is accompanied by of silt. Since the 1940s, dams, barrages and irrigation works have been constructed on the river Indus. The Indus Basin Irrigation System is the "largest contiguous irrigation system developed over the past 140 years" anywhere in the world.
This has reduced the flow of water and by 2018, the average annual flow of water below the Kotri barrage was , and annual amount of silt discharged was estimated at . As a result, the 2010 Pakistan floods were considered "good news" for the ecosystem and population of the river delta as they brought much needed fresh water. Any further utilization of the river basin water is not economically feasible. Vegetation and wildlife of the Indus delta are threatened by the reduced inflow of fresh water, along with extensive deforestation, industrial pollution and global warming. Damming has also isolated the delta population of Indus river dolphins from those further upstream.
Effects of climate change on the river The Tibetan Plateau contains the world's third-largest store of ice. Qin Dahe, the former head of the China Meteorological Administration, said the recent fast pace of melting and warmer temperatures will be good for agriculture and tourism in the short term, but issued a strong warning: "Temperatures are rising four times faster than elsewhere in China, and the Tibetan glaciers are retreating at a higher speed than in any other part of the world... In the short term, this will cause lakes to expand and bring floods and mudflows.. In the long run, the glaciers are vital lifelines of the Indus River.
Once they vanish, water supplies in Pakistan will be in peril." "There is insufficient data to say what will happen to the Indus," says David Grey, the World Bank's senior water advisor in South Asia. "But we all have very nasty fears that the flows of the Indus could be severely, severely affected by glacier melt as a consequence of climate change," and reduced by perhaps as much as 50 percent. "Now what does that mean to a population that lives in a desert [where], without the river, there would be no life? I don't know the answer to that question," he says.
"But we need to be concerned about that. Deeply, deeply concerned." U.S. diplomat Richard Holbrooke said, shortly before his death in 2010, that he believed that falling water levels in the Indus River "could very well precipitate World War III." Pollution Over the years factories on the banks of the Indus River have increased levels of water pollution in the river and the atmosphere around it. High levels of pollutants in the river have led to the deaths of endangered Indus river dolphin. The Sindh Environmental Protection Agency has ordered polluting factories around the river to shut down under the Pakistan Environmental Protection Act, 1997.
Death of the Indus river dolphin has also been attributed to fishermen using poison to kill fish and scooping them up. As a result, the government banned fishing from Guddu Barrage to Sukkur. The Indus is second among a group of ten rivers responsible for about 90% of all the plastic that reaches the oceans. The Yangtze is the only river contributing more plastic. 2010 floods Frequently, Indus river is prone to moderate to severe flooding. In July 2010, following abnormally heavy monsoon rains, the Indus River rose above its banks and started flooding. The rain continued for the next two months, devastating large areas of Pakistan.
In Sindh, the Indus burst its banks near Sukkur on 8 August, submerging the village of Mor Khan Jatoi. In early August, the heaviest flooding moved southward along the Indus River from severely affected northern regions toward western Punjab, where at least of cropland was destroyed, and the southern province of Sindh. , over two thousand people had died and over a million homes had been destroyed since the flooding began. 2011 floods The 2011 Sindh floods began during the Pakistani monsoon season in mid-August 2011, resulting from heavy monsoon rains in Sindh, eastern Balochistan, and southern Punjab. The floods caused considerable damage; an estimated 434 civilians were killed, with 5.3 million people and 1,524,773 homes affected.
Sindh is a fertile region and often called the "breadbasket" of the country; the damage and toll of the floods on the local agrarian economy was said to be extensive. At least of arable land were inundated. The flooding followed the previous year's floods, which devastated a large part of the country. Unprecedented torrential monsoon rains caused severe flooding in 16 districts of Sindh. Barrages, bridges, levees and dams In Pakistan currently there are three barrages on the Indus: Guddu barrage, Sukkur Barrage, and Kotri barrage (also called Ghulam Muhammad barrage). Another new barrage called "Sindh barrage" is planned as terminal barrage on Indus River.
There are some bridges on river Indus, such as, Dadu Moro Bridge, Larkana Khairpur Indus River Bridge, Thatta-Sujawal bridge, Jhirk-Mula Katiar bridge and recently planned Kandhkot-Ghotki bridge. Kala Bagh Barrage, Chasma Barrage, and Taunsa Barrage are also built in Punjab on the Indus. The entire left bank of Indus river in Sind province is protected from river flooding by constructing around 600 km long levees. The right bank side is also leveed from Guddu barrage to Lake Manchar. In response to the levees construction, the river has been aggrading rapidly over the last 20 years leading to breaches upstream of barrages and inundation of large areas.
Tarbela Dam in Pakistan is constructed on the Indus River, while the controversial Kalabagh dam is also being constructed on Indus river. Pakistan is also building Munda Dam. Gallery See also Chura Sharif Ghaggar-Hakra River Geology of the Himalaya HMS Indus Indus Valley Civilisation Rivers of Jammu and Kashmir Sarasvati River Sind Sagar Doab Sindhology Sindhu Darshan Festival Sindhu Pushkaram Rigvedic rivers References Citations Sources Albinia, Alice. (2008) Empires of the Indus: The Story of a River. First American Edition (20101) W. W. Norton & Company, New York. . World Atlas, Millennium Edition, p. 265. Jean Fairley, "The Lion River", Karachi, 1978.
External links The origins of Indus: Gar river basin, Sengge river basin Blankonthemap The Northern Kashmir Website Bibliography on Water Resources and International Law Peace Palace Library Northern Areas Development Gateway The Mountain Areas Conservancy Project Indus River watershed map (World Resources Institute) Indus Treaty Baglihar Dam issue Indus First raft and kayak descents of the Indus headwaters in Tibet Pulitzer Center on Crisis Reporting's project on water issues in South Asia Category:History of Sindh Category:Indus Valley Civilisation Category:International rivers of Asia Category:Rigvedic rivers Category:Rivers of China Category:Rivers of Gilgit-Baltistan Category:Rivers of India Category:Rivers of Jammu and Kashmir Category:Rivers of Pakistan Category:Rivers of Sindh Category:Rivers of the Tibet Autonomous Region Category:Sacred rivers Category:Sarasvati River Category:Rivers in Buddhism Category:Rivers of Khyber Pakhtunkhwa Category:Rivers of Punjab (Pakistan)
The Dickinson System was a mathematical point formula that awarded national championships in college football. Devised by University of Illinois economics professor Frank G. Dickinson, the system crowned national champions from 1926 to 1940, and included predated rankings for 1924 and 1925. The system was originally designed to rank teams in the Big Nine (later the Big Ten) conference. Chicago clothing manufacturer Jack Rissman then persuaded Dickinson to rank the nation's teams under the system, and awarded the Rissman Trophy to the winning university. The Dickinson System was the first to gain widespread national public and media acceptance as a "major selector", according to the NCAA Football Records Book prior to the establishment of the Associated Press poll in 1936.
Dickinson System champions were awarded the Rissman National Trophy, named after Chicago clothing manufacturer Jack Rissman. The trophy was retired in 1930 by Notre Dame, and later the Knute Rockne Intercollegiate Memorial Trophy. Methodology An explanation for the mathematical calculations was usually given as part of the story of the season ending rankings. In 1927, the AP story about the "national football championship" for that year noted that "Scores of 96 football teams were compiled by Dr. Dickinson in seven football conferences, including an Eastern group of 25 leading teams regarded for convenience as a conference... "The Dickinson system awards 30 points for a victory over a strong team, and 20 for victory over a weak team.
Defeats count half as much as victories [15 pts vs. strong team, 10 pts vs. weak team], and ties are considered as games half won and half lost [22.5 points vs. strong, 15 vs. weak]. Dividing this total by the number of games played gives the final rating." Professor Dickinson later added another variable, a "sectional rating" which provided for different points in games where the teams were from different sections of the country. National champions References Category:College football championships Category:College football awards organizations
Bridge No. 122, spanning the Santiago River near Naguabo, Puerto Rico, is significant as "one of the earliest and most elegant examples of concrete beam bridges in Puerto Rico". Built in 1918, it was "futuristic" for its time and has noteworthy architectural detail relative to others. It was designed by Rafael Nones and built by Felix Benitez-Rexach, both engineers, both regarded as masters in their work. Its construction was financed by Puerto Rico's second public bond issue for public works, in 1916, which raised $2 million. The bridge was modified in 1967 but remains the best-preserved example of its type in Puerto Rico.
The bridge has a span, a total length of , and a roadway width of . It was identified as historically important in a review of Puerto Rico's 640 pre-1945 bridges in 1994, and was listed on the National Register of Historic Places in 1995. See also Las Cabanas Bridge, another joint work of Nones and Benitez-Rexach References External links , National Register of Historic Places cover documentation Category:Bridges completed in 1918 Category:Road bridges on the National Register of Historic Places in Puerto Rico Category:Concrete bridges in the United States Category:1918 establishments in Puerto Rico
Alpha Bâ (born 28 May 1989) is a Senegalese football player, who most recently played for ASC Diaraf in the Senegal Premier League. Career Alpha Bâ began his career with US Ouakam. He got a contract with KAA Gent in Belgium in the winter 2010/11. On 20 August 2014 he signed a contract with HB Køge in the Danish 1st Division. References External links Alpha Bâ at Footballdatabase Category:1989 births Category:Living people Category:Senegalese footballers Category:Senegalese expatriate footballers Category:Senegalese expatriate sportspeople in Belgium Category:Belgian First Division A players Category:K.A.A. Gent players Category:HB Køge players Category:Association football midfielders
Portrait of an Elderly Man or Portrait of an Old Nobleman (Spanish - Retrato de caballero anciano) is a 1597-1600 oil on canvas portrait by El Greco, now in the Prado Museum. Its subject's name is unknown but he probably came from Toledo, where the artist was then working. It was stored in the basement of the Real Alcázar of Madrid. References Elderly Man Elderly Man category:16th-century portraits category:1590s paintings Category:Paintings by El Greco in the Museo del Prado
Enter or ENTER may refer to: Enter key, on computer keyboards Enter, Netherlands, a village in the eastern Netherlands Enter (Russian Circles album) Enter (Within Temptation album) Enter, an album by DJ Kentaro Enter (magazine), an American technology magazine for children Enter (Finnish magazine), a Finnish computer magazine Equivalent National Tertiary Entrance Rank (ENTER), an Australian school student assessment Enter Air, a Polish airline. See also Entrance (disambiguation) Entry (disambiguation) Access (disambiguation)
Port of Arkhangelsk () is a major seaport at Arkhangelsk, located at the mouth of the Northern Dvina River, 50 km from the Dvina Bay of the White Sea. The important point links with coastal areas of the Russian North. For much of Russia's history this was Russia's main centre of international maritime trade, conducted by the so-called Pomors ("seaside settlers") from Kholmogory. During the Soviet period it was a major naval and submarine base of the Soviet Navy. It is still a major naval base of the Northern Fleet of the Russian Navy. Overview Arkhangelsk sea port sends and receives lumber, pulp, coal, machinery, metals, industrial and consumer goods.
Arkhangelsk seaport - the main base of the Northern Company, performing the maritime transport of the White, Barents and Kara seas, the Northern Sea Route and overseas lines. Originate from Arkhangelsk regular passenger line to Murmansk, Dikson, Onega, Mezen, Kandalaksha and Novaya Zemlya. As part of the port has 3 cargo area, a container terminal, shipping company "Portoflot" sea-river station. The total length of wharfage - 3.3 km. Berths allow you to take and put handle vessels with a draft of 9.2 m and a length of 175–200 m total usable area for warehousing - 292,000 m², including closed storage - 40,000 m², open tarmac - 250 000 m².
Customs warehouses 2000m ². In Arkhangelsk port is the only container terminal in the North, including the open space area of 98,000 m², which can contain 5762 TEUs at the same time, including up to 200 reefer containers and 2,200 containers with dangerous goods. Bandwidth container terminal 75000 TEUs per year. External links Location of vessels in the port of Arkhangelsk References Arkhangelsk Category:Buildings and structures in Arkhangelsk Arkhangelsk
C (, as in the letter c) is a general-purpose, procedural computer programming language supporting structured programming, lexical variable scope, and recursion, while a static type system prevents unintended operations. By design, C provides constructs that map efficiently to typical machine instructions and has found lasting use in applications previously coded in assembly language. Such applications include operating systems and various application software for computers, from supercomputers to PLCs and, to embedded systems. C was originally developed at Bell Labs by Dennis Ritchie between 1972 and 1973 to make utilities running on Unix. Later, it was applied to re-implementing the kernel of the Unix operating system.
During the 1980s, C gradually gained popularity. It has become one of the most widely used programming languages, with C compilers from various vendors available for the majority of existing computer architectures and operating systems. C has been standardized by the ANSI since 1989 (see ANSI C) and by the International Organization for Standardization. C is an imperative procedural language. It was designed to be compiled using a relatively straightforward compiler to provide low-level access to memory and language constructs that map efficiently to machine instructions, all with minimal runtime support. Despite its low-level capabilities, the language was designed to encourage cross-platform programming.
A standards-compliant C program written with portability in mind can be compiled for a wide variety of computer platforms and operating systems with few changes to its source code. The language is available on various platforms, from embedded microcontrollers to supercomputers. Overview Like most procedural languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion. Its static type system prevents unintended operations. In C, all executable code is contained within subroutines (also called "functions", though not strictly in the sense of functional programming). Function parameters are always passed by value. Pass-by-reference is simulated in C by explicitly passing pointer values.
C program source text is free-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements. The C language also exhibits the following characteristics: The language has a small, fixed number of keywords, including a full set of control flow primitives: if/else, for, do/while, while, and switch. User-defined names are not distinguished from keywords by any kind of sigil. It has a large number of arithmetic, bitwise, and logic operators: +, +=, ++, &, ||, etc. More than one assignment may be performed in a single statement. Functions: Function return values can be ignored, when not needed.
Function and data pointers permit ad hoc run-time polymorphism. Functions may not be defined within the lexical scope of other functions. Data typing is static, but weakly enforced; all data has a type, but implicit conversions are possible. Declaration syntax mimics usage context. C has no "define" keyword; instead, a statement beginning with the name of a type is taken as a declaration. There is no "function" keyword; instead, a function is indicated by the presence of a parenthesized argument list. User-defined (typedef) and compound types are possible. Heterogeneous aggregate data types (struct) allow related data elements to be accessed and assigned as a unit.
Union is a structure with overlapping members; only the last member stored is valid. Array indexing is a secondary notation, defined in terms of pointer arithmetic. Unlike structs, arrays are not first-class objects: they cannot be assigned or compared using single built-in operators. There is no "array" keyword in use or definition; instead, square brackets indicate arrays syntactically, for example month[11]. Enumerated types are possible with the enum keyword. They are freely interconvertible with integers. Strings are not a distinct data type, but are conventionally implemented as null-terminated character arrays. Low-level access to computer memory is possible by converting machine addresses to typed pointers.
Procedures (subroutines not returning values) are a special case of function, with an untyped return type void. A preprocessor performs macro definition, source code file inclusion, and conditional compilation. There is a basic form of modularity: files can be compiled separately and linked together, with control over which functions and data objects are visible to other files via static and extern attributes. Complex functionality such as I/O, string manipulation, and mathematical functions are consistently delegated to library routines. While C does not include certain features found in other languages (such as object orientation and garbage collection), these can be implemented or emulated, often through the use of external libraries (e.g., the GLib Object System or the Boehm garbage collector).
Relations to other languages Many later languages have borrowed directly or indirectly from C, including C++, C#, Unix's C shell, D, Go, Java, JavaScript (including transpilers), Limbo, LPC, Objective-C, Perl, PHP, Python, Rust, Swift, Verilog and SystemVerilog (hardware description languages). These languages have drawn many of their control structures and other basic features from C. Most of them (Python being a dramatic exception) also express highly similar syntax to C, and they tend to combine the recognizable expression and statement syntax of C with underlying type systems, data models, and semantics that can be radically different. History Early developments The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-7 by Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues.
Eventually, they decided to port the operating system to a PDP-11. The original PDP-11 version of Unix was also developed in assembly language. Thompson desired a programming language to make utilities for the new platform. At first, he tried to make a Fortran compiler, but soon gave up the idea. Instead, he created a cut-down version of the recently developed BCPL systems programming language. The official description of BCPL was not available at the time, and Thompson modified the syntax to be less wordy, producing the similar but somewhat simpler B. However, few utilities were ultimately written in B because it was too slow, and B could not take advantage of PDP-11 features such as byte addressability.
In 1972, Ritchie started to improve B, which resulted in creating a new language C. The C compiler and some utilities made with it were included in Version 2 Unix. At Version 4 Unix, released in November 1973, the Unix kernel was extensively re-implemented in C. By this time, the C language had acquired some powerful features such as struct types. Unix was one of the first operating system kernels implemented in a language other than assembly. Earlier instances include the Multics system (which was written in PL/I) and Master Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961.
In around 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating system. Johnson's Portable C Compiler served as the basis for several implementations of C on new platforms. K&R C In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language. This book, known to C programmers as K&R, served for many years as an informal specification of the language. The version of C that it describes is commonly referred to as "K&R C". The second edition of the book covers the later ANSI C standard, described below.
K&R introduced several language features: Standard I/O library long int data type unsigned int data type Compound assignment operators of the form =op (such as =-) were changed to the form op= (that is, -=) to remove the semantic ambiguity created by constructs such as i=-10, which had been interpreted as i =- 10 (decrement i by 10) instead of the possibly intended i = -10 (let i be -10). Even after the publication of the 1989 ANSI standard, for many years K&R C was still considered the "lowest common denominator" to which C programmers restricted themselves when maximum portability was desired, since many older compilers were still in use, and because carefully written K&R C code can be legal Standard C as well.
In early versions of C, only functions that return types other than int must be declared if used before the function definition; functions used without prior declaration were presumed to return type int. For example: long some_function(); /* int */ other_function(); /* int */ calling_function() { long test1; register /* int */ test2; test1 = some_function(); if (test1 > 0) test2 = 0; else test2 = other_function(); return test2; } The int type specifiers which are commented out could be omitted in K&R C, but are required in later standards. Since K&R function declarations did not include any information about function arguments, function parameter type checks were not performed, although some compilers would issue a warning message if a local function was called with the wrong number of arguments, or if multiple calls to an external function used different numbers or types of arguments.
Separate tools such as Unix's lint utility were developed that (among other things) could check for consistency of function use across multiple source files. In the years following the publication of K&R C, several features were added to the language, supported by compilers from AT&T (in particular PCC) and some other vendors. These included: void functions (i.e., functions with no return value) functions returning struct or union types (rather than pointers) assignment for struct data types enumerated types The large number of extensions and lack of agreement on a standard library, together with the language popularity and the fact that not even the Unix compilers precisely implemented the K&R specification, led to the necessity of standardization.
ANSI C and ISO C During the late 1970s and 1980s, versions of C were implemented for a wide variety of mainframe computers, minicomputers, and microcomputers, including the IBM PC, as its popularity began to increase significantly. In 1983, the American National Standards Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the non-portable portion of the Unix C library was handed off to the IEEE working group 1003 to become the basis for the 1988 POSIX standard. In 1989, the C standard was ratified as ANSI X3.159-1989 "Programming Language C".
This version of the language is often referred to as ANSI C, Standard C, or sometimes C89. In 1990, the ANSI C standard (with formatting changes) was adopted by the International Organization for Standardization (ISO) as ISO/IEC 9899:1990, which is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the same programming language. ANSI, like other national standards bodies, no longer develops the C standard independently, but defers to the international C standard, maintained by the working group ISO/IEC JTC1/SC22/WG14. National adoption of an update to the international standard typically occurs within a year of ISO publication. One of the aims of the C standardization process was to produce a superset of K&R C, incorporating many of the subsequently introduced unofficial features.
The standards committee also included several additional features such as function prototypes (borrowed from C++), void pointers, support for international character sets and locales, and preprocessor enhancements. Although the syntax for parameter declarations was augmented to include the style used in C++, the K&R interface continued to be permitted, for compatibility with existing source code. C89 is supported by current C compilers, and most modern C code is based on it. Any program written only in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, within its resource limits. Without such precautions, programs may compile only on a certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte endianness.
In cases where code must be compilable by either standard-conforming or K&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and K&R sections to prevent the use on a K&R C-based compiler of features available only in Standard C. After the ANSI/ISO standardization process, the C language specification remained relatively static for several years. In 1995, Normative Amendment 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally as C95) was published, to correct some details and to add more extensive support for international character sets. C99 The C standard was further revised in the late 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999, which is commonly referred to as "C99".
It has since been amended three times by Technical Corrigenda. C99 introduced several new features, including inline functions, several new data types (including long long int and a complex type to represent complex numbers), variable-length arrays and flexible array members, improved support for IEEE 754 floating point, support for variadic macros (macros of variable arity), and support for one-line comments beginning with //, as in BCPL or C++. Many of these had already been implemented as extensions in several C compilers. C99 is for the most part backward compatible with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed.
A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 support is available. GCC, Solaris Studio, and other C compilers now support many or all of the new features of C99. The C compiler in Microsoft Visual C++, however, implements the C89 standard and those parts of C99 that are required for compatibility with C++11. C11 In 2007, work began on another revision of the C standard, informally called "C1X" until its official publication on 2011-12-08. The C standards committee adopted guidelines to limit the adoption of new features that had not been tested by existing implementations.
The C11 standard adds numerous new features to C and the library, including type generic macros, anonymous structures, improved Unicode support, atomic operations, multi-threading, and bounds-checked functions. It also makes some portions of the existing C99 library optional, and improves compatibility with C++. The standard macro __STDC_VERSION__ is defined as 201112L to indicate that C11 support is available. C18 Published in June 2018, C18 is the current standard for the C programming language. It introduces no new language features, only technical corrections and clarifications to defects in C11. The standard macro __STDC_VERSION__ is defined as 201710L. Embedded C Historically, embedded C programming requires nonstandard extensions to the C language in order to support exotic features such as fixed-point arithmetic, multiple distinct memory banks, and basic I/O operations.
In 2008, the C Standards Committee published a technical report extending the C language to address these issues by providing a common standard for all implementations to adhere to. It includes a number of features not available in normal C, such as fixed-point arithmetic, named address spaces, and basic I/O hardware addressing. Syntax C has a formal grammar specified by the C standard. Line endings are generally not significant in C; however, line boundaries do have significance during the preprocessing phase. Comments may appear either between the delimiters /* and */, or (since C99) following // until the end of the line.
Comments delimited by /* and */ do not nest, and these sequences of characters are not interpreted as comment delimiters if they appear inside string or character literals. C source files contain declarations and function definitions. Function definitions, in turn, contain declarations and statements. Declarations either define new types using keywords such as struct, union, and enum, or assign types to and perhaps reserve storage for new variables, usually by writing the type followed by the variable name. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ({ and }, sometimes called "curly brackets") to limit the scope of declarations and to act as a single statement for control structures.
As an imperative language, C uses statements to specify actions. The most common statement is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; as a side effect of the evaluation, functions may be called and variables may be assigned new values. To modify the normal sequential execution of statements, C provides several control-flow statements identified by reserved keywords. Structured programming is supported by if(-else) conditional execution and by do-while, while, and for iterative execution (looping). The for statement has separate initialization, testing, and reinitialization expressions, any or all of which can be omitted. break and continue can be used to leave the innermost enclosing loop statement or skip to its reinitialization.
There is also a non-structured goto statement which branches directly to the designated label within the function. switch selects a case to be executed based on the value of an integer expression. Expressions can use a variety of built-in operators and may contain function calls. The order in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may even be interleaved. However, all side effects (including storage to variables) will occur before the next "sequence point"; sequence points include the end of each expression statement, and the entry to and return from each function call.
Sequence points also occur during evaluation of expressions containing certain operators (&&, ||, ? : and the comma operator). This permits a high degree of object code optimization by the compiler, but requires C programmers to take more care to obtain reliable results than is needed for other programming languages. Kernighan and Ritchie say in the Introduction of The C Programming Language: "C, like any other language, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be better." The C standard did not attempt to correct many of these blemishes, because of the impact of such changes on already existing software.
Character set The basic C source character set includes the following characters: Lowercase and uppercase letters of ISO Basic Latin Alphabet: a–z A–Z Decimal digits: 0–9 Graphic characters: ! " # % & ' ( ) * + , - . / : ; < = > ? [ \ ] ^ _ { | } ~ Whitespace characters: space, horizontal tab, vertical tab, form feed, newline Newline indicates the end of a text line; it need not correspond to an actual single character, although for convenience C treats it as one. Additional multi-byte encoded characters may be used in string literals, but they are not entirely portable.