Programming: Parameters of Subroutines

Introduction to Parameters of Subroutines

A subroutine (also known as a method, procedure, function, or routine) is a set of instructions grouped together to perform a specific task within a program.
A parameter is a variable used by a subroutine to receive a piece of information that it needs to carry out its task.
Parameters are placed within the parentheses following the subroutine’s name, and multiple parameters are separated by commas.

Formal and Actual Parameters

Formal parameters are the parameter names and data types listed in the subroutine declaration.
Actual parameters (also called arguments) are the specific values or variables that the subroutine is called with in the actual code.
During a subroutine call, the actual parameters are matched with the formal parameters in order, from left to right.

Parameter Passing Methods

Pass-by-value: The parameter’s value is copied into the formal parameter of the subroutine. In this case, changes made within the subroutine don’t affect the original variable.
Pass-by-reference: Rather than providing a copy, a reference to the original variable is used. This means that any changes made within the subroutine will also change the original variable.

Default Parameters and Optional Parameters

A default parameter has a value assigned to it within the subroutine definition. This value is used if no value is provided when calling the subroutine.
Optional parameters are parameters that can be omitted when the subroutine is called.
Default and optional parameters allow more flexible subroutine calls and can help to simplify code.

Python Example

A function in Python might be defined with parameters like so: def hello(name): print("Hello, " + name)
This function can then be called with an argument like so: hello("World")

Understanding how to use parameters within subroutines is key to creating effective and reusable code. It forms a significant part of procedural programming, leveraging the strength of subroutines to prevent repetition and improve the structure of a program.