Show description

Procedures playa fundamental role in program design. They aid in displaying the algorithm's structure and in decomposing a program into logically coherent units. e. of long programs. In the above example, it might be considered somewhat extravagant to declare separate procedures instead of merely substituting the refined program texts for the identifiers. Nevertheless, the gain in clarity of program structure often recommends the use of explicit procedures even in such a simple case. But of course procedures become particularly useful, if the same procedure is to be invoked at several points of the program.

There is no universally accepted standard for this purpose. We shall denote the control character signifying a line end by the identifier EOl (end of line); its actual value depends on the system used. In order to be able to denote non-printable characters, Modula uses their octal ordinal number followed by the capital letter C. For example, 14C is a value of type CHAR denoting the control character ff (form feed) with ordinal number 14B. 6 The Type BITSET The values which belong to the type BITSET are sets of integers between 0 and N-1, where N is a constant defined by the computer system used.

If, for example, we wish to find the index of an element equal to a given value x, we have no advance knowledge how many elements have to be inspected. Hence, the use of a while (or repeat) statement is recommended. This algorithm is known as linear search. i := 0; WHILE (i i := i+1 END < N) & (ali] # x) DO From the negation of the continuation condition, applying de Morgan's law, we infer that upon termination of the while statement the condition (i=N) OR (a[i]=x) holds. If the latter term is TRUE, the desired element is found and i is its index; if i = N, no a[i] equals x.