Functions and procedures

Functions are subprograms that return a value. Procedures are subprograms that do not return the value.

The following sample illustrates declaration of two procedures; one of them takes no arguments, and another procedure takes 2 arguments:

  program procedureSample;
  var n: integer; { this variable is visible in main 
                    program block and in all functions 
                    and procedures }

  procedure noArgs;
  begin
    n := 5;
  end;

  procedure twoArgs(a: integer; b: string);
  var len: integer; { this variable can be accessed only 
                      from within the procedure and is 
                      reinitialized every time that the 
                      procedure is called }
  begin
    len := length(b);
    n := a + len;
  end;

  begin
    noArgs; { call the first procedure }
    twoArgs(n, 'Some string'); { call the second procedure }
  end.

Functions are similar to procedures, except that they can return values. The following sample illustrates the use of the functions in MIDletPascal:

  program functionSample;
  var result: integer;

  { this simple function always returns 5 }
  function returnFive: integer;
  begin
    returnFive := 5;
  end;

  function multiply(a, b: integer): integer;
  begin
    multiply := a * b;
  end;

  begin
    result := multiply(2, returnFive); { call the multiply function 
                                         where on argument is value 
                                         returned by calling the 
                                         other function }
  end.

Recursion is also allowed:

  program recursionSample;
  var factorielOfFive: integer;
  function factoriel(n: integer): integer;
  begin
    if n = 1 then 
      factoriel := 1;
    else
      factoriel := n * factoriel(n-1);
  end;

  begin
    factorielOfFive := factoriel(5);
  end.

Differences from standard Pascal language:

• procedures and functions cannot be nested, i.e. one function cannot be declared inside the other function
• variable parameters are not supported

MIDletPascal supports forward references. Consider the following program:

  procedure a (x: integer);
  begin
    ...
    b(x);
    ...
  end;

  procedure b(y: integer);
  begin
  ...
    a(y);
  ...
  end;

  begin
    a(5);
  end.

Procedure a calls procedure b, and procedure b calls procedure a. When procedure b call procedure a, everything is OK, because the procedure a appears before procedure b. But compiler will report an error in procedure a, because it calls procedure that has not been declared yet. To solve this problem, use the forward reference:

  procedure b(y:integer); forward; { the forward reference tells 
                                     compiler that procedure 'b' will 
                                     be defined somewhere in the program code }

  procedure a (x: integer);
  begin
    ...
    b(x);
    ...
  end;

  procedure b(y: integer);
  begin
    ...
    a(y);
    ...
  end;

  begin
    a(5);
  end.