# Defining a Subroutine

## Introduction

A subroutine is a set of common tasks that can be defined once and called multiple times from within a PGM. A subroutine is also a convenient way of grouping a set of tasks making code more legible.

A subroutine is similar to a function but does not return a result. So unlike a function it can not be included in an expression. A subroutine can be used instead of a function if a value does not need to be returned. If a value does need to be returned then a function will need to be used.

## Syntax

Sub subName (argument list)
...statements...
EndSub


subName : is an unique name of the function, used to refer to the function.
argument list : optional list of parameters in the following format :

...datatype parameterName, datatype parameterName...etc
• The subroutine declaration must begin with the Sub keyword and end with the EndSub keyword.
• A subroutine may call itself (ie recursive subroutines are allowed). However, a true stack of the subroutine variables is not used.
• In contrast to a function, a Return statement cannot be used/is not required.
• The parameter list cannot include instance of classes or variables passed by reference.
• Empty parentheses must be inserted, if no parameters are required by the subroutine.
• Local variables can be declared within the subroutine, and their scope is limited to the subroutine. However when a subroutine calls itself recursively a local stack is not used.
• Subroutine definitions cannot be nested (ie subroutines cannot be defined within subroutines).

## Examples and Use

Subroutine Examples

Example 1

 Sub CapacityCheck(Str unit, real capacity)
Str Feed_tag
Feed_tag = Concatenate(unit, "QFeed.Qm (t/h)")
If ([Feed_tag] > capacity)
Lognote(Concatenate(unit, " has exceeded its capacity"))
Endif
EndSub


Using Subroutines...

;check capacity of unit using subroutine
CapacityCheck("Spiral_1", 20)