Functions

CSCI 150, Spring 2003

Procedures and Functions

1. Procedures with more than one parameter.
All formal parameters are listed in the parentheses following the procedure name. There can be as many as you need. When the procedure is called, the actual parameters are matched to the formal parameters in the order they are listed. There must be the same number of actual parameters as there are formal parameters and they must have matching types.

Example:

program calcCube;
procedure Cube( n: integer; var result: integer);
begin
	result := n * n * n;
end;
var
	number: integer;
	answer: integer;
begin
	writeln('Enter a number: ');
	readln(number);
	Cube(number, answer);
	writeln('The cube of ', number, ' is ', answer);
end.

2. Procedures with local variables.
A procedure may have local variables in addition to the parameters. The local variables are listed just below the procedure header. The variables are local to the procedure, so they cannot be accessed by any other procedure or by the main program.

Example:

program volumeFinder;
procedure WriteVolume( r, h: real );
var 
	volume: real;
begin
	volume := 3.14159 * r * r * h;
	writeln( 'The volume is ', volume);
end;
var
	radius, height: real;
begin
	writeln('Enter the radius and height: ');
	readln(radius);
	readln(height);
	WriteVolume( radius, height );
end.

3. Functions.
Functions are subprograms that return a value. They behave like procedures in most respects, except they return a value to the calling program. The type of value returned is specified at the end of the function header. The name of the function is used like a variable within the function definition. At the end of the function execution the value of this identifier is returned to the calling program.

Example:

program calcCube;
function Cube( n: integer ): integer;	{Return a value of type integer }
begin
	Cube := n * n * n;	{the value of Cube will be returned }
end;
var
	number: integer;
begin
	writeln('Enter a number: ');
	readln(number);
	writeln('The cube of ', number, ' is ', Cube(number));
end.

Another Example:

program circles;
function Area( r: real ): real;
begin
	Area := 3.14159 * r * r;
end;
var
	materialCost: real;
	radius: real;
	totalCost: real;
begin
	writeln('Enter the radius of the circle: ');
	readln(radius);
	writeln('Enter the cost of the material: ');
	readln(materialCost);
	totalCost := Area( radius ) * materialCost;
	writeln('The total cost to fill the circle with the material is ', totalCost:10:2);
end.