Procedures and Functions

A procedure is a named block of code that performs a task without returning a value. It is invoked using the CALL keyword.

Defining a procedure

A procedure with no parameters:

PROCEDURE ProcedureName
   // statements that do the work
ENDPROCEDURE

A procedure with parameters (values passed in):

PROCEDURE ProcedureName(Param1 : TYPE, Param2 : TYPE, ...)
   // statements that use the parameters
ENDPROCEDURE

Each parameter is named and given a data type, so the procedure knows what kind of value to expect.

Calling a procedure

Procedures are run using the CALL keyword:

CALL ProcedureName
CALL ProcedureName(Value1, Value2)

The values in brackets are called arguments. Each argument is matched in order to the corresponding parameter in the procedure's definition.

Example — calculate-area procedure

PROCEDURE CalculateArea(Length : INTEGER, Width : INTEGER)
   Area ← Length * Width
   OUTPUT "The area is ", Area
ENDPROCEDURE

// Main program
CALL CalculateArea(5, 3)

When CALL CalculateArea(5, 3) is executed:

1. The procedure receives Length = 5 and Width = 3.
2. It calculates Area = 5 * 3 = 15.
3. It outputs The area is 15.
4. Control returns to the line after the CALL.

The procedure does its job (outputting the area), but it does not give a value back for the caller to use. The caller cannot say X ← CalculateArea(5, 3).

When to use a procedure

Choose a procedure when the sub-program's job is to do something rather than to compute and return something:

• Show a menu on screen.
• Save data to a file.
• Display a report.
• Reset all the variables to a known starting state.