Procedures and Functions

A function is a named block of code that performs a calculation and returns a value to the place it was called from. It is called directly inside an expression, not with CALL.

Defining a function

A function with no parameters:

FUNCTION FunctionName RETURNS TYPE
   // statements
   RETURN Value
ENDFUNCTION

A function with parameters:

FUNCTION FunctionName(Param1 : TYPE, Param2 : TYPE, ...) RETURNS TYPE
   // statements
   RETURN Value
ENDFUNCTION

Two extra things compared with a procedure:

1. The keyword RETURNS <data type> appears at the end of the first line, declaring what type of value the function gives back.
2. Inside the body, a RETURN <value> statement specifies the value to send back. The function ends as soon as a RETURN runs.

Calling a function

A function is not called with CALL. It is used inside an expression, in any place a value would normally go:

Result ← FunctionName(Value1, Value2)
OUTPUT FunctionName(5, 3)
IF FunctionName(X) > 0 THEN
   ...
ENDIF

The expression FunctionName(...) evaluates to whatever the function returned.

Example — calculate-area function

FUNCTION CalculateArea(Length : INTEGER, Width : INTEGER) RETURNS INTEGER
   Area ← Length * Width
   RETURN Area
ENDFUNCTION

// Main program: use the returned value
OUTPUT CalculateArea(5, 3)            // outputs 15

// Or save it for later use
Result ← CalculateArea(10, 20)
OUTPUT "The area is ", Result          // outputs "The area is 200"

The function gives back Area to the caller. The caller can output it, save it in a variable, use it inside another calculation, or pass it as an argument to a different sub-program.

When to use a function

Choose a function when the sub-program's job is to calculate and produce a value:

• Calculate the area of a rectangle.
• Convert a temperature from Celsius to Fahrenheit.
• Return the largest of a list of numbers.
• Look up a student's grade from their mark.
• Check whether a password meets the validation rules (returning TRUE or FALSE).