Procedures accept data or variables when they are executed. Functions also accept data, but have the ability to return a value to the procedure or program which requests it. Functions are used to perform mathematical tasks like factorial calculations.

A function

• begins with the keyword function
  
• is similar in structure to a procedure
  
• somewhere inside the code associated with the function, a value is assigned to the function name
  
• a function is used on the righthand side of an expression
  
• can only return a simple data type

The actual heading of a function differs slightly than that of a procedure. Its format is,

      function  Function_name (variable declarations) : return_data_type;

After the parenthesis which declare those variables accepted by the function, the return data type (preceeded by a colon) is declared.

	function  ADD_TWO ( value1, value2 : integer ) : integer;

	begin

	     ADD_TWO := value1 + value2

	end;

The following line demonstrates how to call the function,

	result := ADD_TWO( 10, 20 );

thus, when ADD_TWO is executed, it equates to the value assigned to its name (in this case 30), which is then assigned to result.

---

SELF TEST
Determine the output of the following program

	program  function_time (input, output);

	const    maxsize = 80;

	type     line = packed array[1..maxsize] of char;

	function COUNTLETTERS ( words : line) : integer; {returns an integer}

	var      loop_count : integer;                   {local variable}

	begin

	      loop_count := 1;

	      while (words[loop_count] <> '.') and (loop_count <= maxsize) do

		      loop_count := loop_count + 1;

	      COUNTLETTERS := loop_count - 1

	end;
	var   oneline : line;

	      letters : integer;

	begin

	      writeln('Please enter in a sentence terminated with a .');

	      readln( oneline );

	      letters := COUNTLETTERS( oneline );

	      writeln('There are ',letters,' letters in that sentence.')

	end.