Procedures and functions

Defining and calling procedures

A procedure with no parameters is defined as follows:

PROCEDURE <identifier>
    <statement(s)>
ENDPROCEDURE

A procedure with parameters is defined as follows:

PROCEDURE <identifier>(<param1> : <data type>, <param2> : <data type>...)
    <statement(s)>
ENDPROCEDURE

The <identifier> is the identifier used to call the procedure. Where used, param1, param2 etc. are identifiers for the parameters of the procedure. These will be used as variables in the statements of the procedure.

Procedures defined as above should be called as follows, respectively:

CALL <identifier>
CALL <identifier>(Value1, Value2, ...)

These calls are complete program statements.

When parameters are used, Value1, Value2... must be of the correct data type and in the same sequence as in the definition of the procedure.

Unless otherwise stated, it should be assumed that parameters are passed by value. (See section 8.3).

//Example – definition and use of procedures with and without parameters
PROCEDURE DefaultSquare
    CALL Square(100)
ENDPROCEDURE

PROCEDURE Square(Size : INTEGER)
    FOR Side ← 1 TO 4
           CALL MoveForward(Size)
           CALL Turn(90)
    NEXT Side
ENDPROCEDURE

IF Size = Default THEN
    CALL DefaultSquare
ELSE
    CALL Square(Size)
ENDIF

Defining and calling functions

Functions operate in a similar way to procedures, except that in addition they return a single value to the point

at which they are called. Their definition includes the data type of the value returned. A function with no parameters is defined as follows:

FUNCTION <identifier> RETURNS <data type>
    <statement(s)>
ENDFUNCTION

A function with parameters is defined as follows:

FUNCTION <identifier>(<param1> : <data type>, <param2> : <data type>...) RETURNS <data type>
    <statement(s)>
ENDFUNCTION

The keyword RETURN is used as one of the statements within the body of the function to specify the value to be returned. Normally, this will be the last statement in the function definition, however, if the RETURN statement is in the body of the function its execution is immediate and any subsequent lines of code are omitted.

Because a function returns a value that is used when the function is called, function calls are not complete program statements. The keyword CALL should not be used when calling a function. Functions should only be called as part of an expression. When the RETURN statement is executed, the value returned replaces the function call in the expression and the expression is then evaluated.

//Example – definition and use of a function
FUNCTION Max(Number1 : INTEGER, Number2 : INTEGER) RETURNS INTEGER
    IF Number1 > Number2 THEN
        RETURN Number1
    ELSE
        RETURN Number2
    ENDIF
ENDFUNCTION

OUTPUT "Penalty Fine = ", Max(10, Distance*2)

def {function}（{parameters}):
	{statements}
	return {value}

def factorial(number):
	result = 1
	for i in range(1, number + 1):
		result = result * i
	return result
f1 = factorial(5)
f2 = factorial(10)
print(f1)
print(f2)

Passing parameters by value or by reference

To specify whether a parameter is passed by value or by reference, the keywords BYVAL and BYREF precede the parameter in the definition of the procedure. If there are several parameters passed by the same method, the BYVAL or BYREF keyword need not be repeated.

//Example – passing parameters by reference
PROCEDURE SWAP(BYREF X : INTEGER, Y : INTEGER)
    Temp ← X
    X ← Y
    Y ← Temp
ENDPROCEDURE

If the method for passing parameters is not specified, passing by value is assumed. How this should be called and how it operates has already been explained in Section 8.1.

Parameters should not be passed by reference to a function.