Functions and Procedures as Subroutines

• The topic considers functions and procedures as subroutines.
• Dr. Belgroun Brahim from the University of Khenchela created this course for 1st-year MI, Math, & INFO in 2022/2023.

Introduction to Subroutines

• Tackling complex problems requires breaking them into simpler sub-problems via a bottom-up approach.
• Programs can be divided into reusable pieces, which can be extracted and processed independently.
• Subroutines refer to functions and procedures.

Combination Example Overview

• Combination algorithms can be broken down into similar parts.
• The key difference lies in numbers within the "for" loop, considered an attribute of the new part.
• The Fact function calculates the factorial of a number and returns an integer.

Function Details

• A function is a subroutine that returns a value of a specified type.
• Functions can accept parameters of various types.
• When invoked, a function acts as an expression that corresponds to the returned value’s type.

How to Utilize Functions

• When a function is called, it's treated as an expression with its returned value type.
• Function parameters can be replaced with global variables of matching types.
• Expressions with compatible types can also serve as function parameters.
• The function name should not be assigned a value using the "=" assignment symbol, as the left part of the assignment should be a variable, not a value.

Procedures Defined

• A procedure is a subroutine for executing a parameterized task and may or may not take inputs, but it does not return a result.

How to Utilize Procedures

• Procedures entail a series of sequentially executed instructions determined by its parameters.
• Procedure parameters can be substituted with global variables or expressions that match the parameter types.
• The procedure name cannot be assigned a value using the "=".
• The returned value must be ignored; it cannot be included in an expression.

Global vs Local Variables

• Each variable possesses a scope, representing a code block where it exists and can be modified.
• Variables can either be local or global.
• A global variable is defined in the main program, and all subroutines can access it.
• A local variable's scope is limited to the subroutine in which it is defined and is created, and then destroyed at the end of execution.
• If a local variable shares a name with a global one, the global variable becomes inaccessible within that routine.
• Subroutine parameters are exceptional local variables known as "formal variables”.
• The difference is that formal parameters are initialized with a value which is the call argument provided by the calling function.

Parameter Passing Methods

• Program division into subroutines allows linked subroutines to work together.
• This involves exchanging parameters between subroutines to achieve the main program's purpose. Methods to pass parameters include:
  • Passing by value: a copy of the value is passed. Modifications inside the subroutine do not affect the original variable.
  • Passing by variable: the actual variable is passed.
  • Passing by address.

Recursion Defined

• For particular problems solvable through a recursive approach, the solution of the next situation is generated from existing known solutions.
• Specifically, recursion is a function that calls itself, which repeats until a stopping criterion is satisfied.
• The process involves a parent function invoking a child function with modified parameters until the final function reaches the specified condition.
• It then sends the appropriate result to its parent, ultimately returning a final result to the original function.

Recursive Properties

• Stopping Condition: Determines the termination point of the recursive calls.
• Resolution: Involving how the result of a parent function is calculated from its child function.
• Recursive call(s): Where parameters are modified according to those of the parent function.