operatorwhich is classified as relational operator following are examples of set expressions and their fully parenthesized equivalentsr + ( *st rst ( *tr + ( -st + ( /tx in in ( + the array structure the array is probably the most widely used data structurein some languages it is even the only one available an array consists of components which are all of the same typecalled its base typeit is therefore called homogeneous structure the array is random-access structurebecause all components can be selected at random and are equally quickly accessible in order to denote an individual componentthe name of the entire structure is augmented by the index selecting the component this index is to be an integer between and - where is the number of elementsthe sizeof the array type array of examples type row array of real type card array of char type name array of char particular value of variable var xrow with all components satisfying the equation xi -imay be visualized as shown in fig fig array of type row with xi - an individual component of an array can be selected by an index given an array variable xwe denote an array selector by the array name followed by the respective component' index iand we write xi or [ibecause of the firstconventional notationa component of an array component is therefore also called subscripted variable the common way of operating with arraysparticularly with large arraysis to selectively update single components rather than to construct entirely new structured values this is expressed by considering an array variable as an array of component variables and by permitting assignments to selected componentssuch as for example [ : although selective updating causes only single component value to changefrom conceptual point of view we must regard the entire composite value as having changed too the fact that array indicesi names of array componentsare integershas most important consequenceindices may be computed general index expression may be substituted in place of an index constantthis expression is to be evaluatedand the result identifies the selected component this