the type boolean the two values of the standard type boolean are denoted by the identifiers true and false the boolean operators are the logical conjunctiondisjunctionand negation whose values are defined in table the logical conjunction is denoted by the symbol &the logical disjunction by orand negation by "~note that comparisons are operations yielding result of type boolean thusthe result of comparison may be assigned to variableor it may be used as an operand of logical operator in boolean expression for instancegiven boolean variables and and integer variables the two assignments : :( < ( zyield false and true or & ~ true true true true false true false true false false false true true false true false false false false true table boolean operators the boolean operators (andand or have an additional property in most programming languageswhich distinguishes them from other dyadic operators whereasfor examplethe sum + is not definedif either or is undefinedthe conjunction & is defined even if is undefinedprovided that is false this conditionality is an important and useful property the exact definition of and or is therefore given by the following equationsp& if then else false or if then true else the type char the standard type char comprises set of printable characters unfortunatelythere is no generally accepted standard character set used on all computer systems thereforethe use of the predicate "standardmay in this case be almost misleadingit is to be understood in the sense of "standard on the computer system on which certain program is to be executed the character set defined by the international standards organization (iso)and particularly its american version ascii (american standard code for information interchangeis the most widely accepted set the ascii set is therefore tabulated in appendix it consists of printable (graphiccharacters and control charactersthe latter mainly being used in data transmission and for the control of printing equipment in order to be able to design algorithms involving characters ( values of type char)that are system independentwe should like to be able to assume certain minimal properties of character setsnamely the type char contains the capital latin lettersthe lower-case lettersthe decimal digitsand number of other graphic characterssuch as punctuation marks the subsets of letters and digits are ordered and contiguousi