Functions in Programming

Functions

• A function is a self-contained program segment that performs specific tasks.
• Functions help make programs modular.
• Functions can be reused in different parts of a program.
• Functions are easier to debug and modify.

Advantages of functions

• Make programs modular
• Structured programming
• Easier to debug algorithms
• Easier code modification
• Reusable in other algorithms

Function Definition

• function_name(parameter_list) is the function header
• { and } define the function body
• Declarations inside the body declare variables used within the function
• Statements inside the body define the actions or tasks the function performs
• return (expression) returns a value from the function

Function Prototypes

• If a function isn't defined before use, declare it by specifying its return type and parameter types.
• If all functions are defined before use, no prototypes are necessary.
• main() is the last function (often) in an algorithm.

Scope Rules for Functions

• Variables declared inside a function are local to that function.
• Other functions can't directly access these variables.
• Variables are passed to functions as parameters.
• Variables are returned from a function via a return statement.

Function Calls

• When a function is called, expressions in its parameter list are evaluated.
• Resulting values are converted to the correct data type for the function.
• Parameters are copied to local variables within the function.
• The function's body executes.
• When a return statement is encountered, the function terminates.
• The value specified in the return statement is passed to the calling function (like main).

Types of Functions

• User-defined functions
• Standard library functions

User-Defined Functions

• Every algorithm must have a main function to define its start.
• Large algorithms can be problematic if only using main().
• Dividing the algorithm into smaller functions (called functional parts) makes debugging, testing, and maintenance easier.
• Repeated calculations can be written as functions for reusability.

Another approach

• Design a function that can be called and used whenever needed, avoiding redundant code.

Function as a black box

• A function is a self-contained block of code that performs a specific task.
• Once created, a function can be treated as a "black box" that takes input from the main algorithm and returns a value.

Return Statement

• The return statement is the mechanism for returning a value to the calling function.
• By default, functions return an integer value.
• Type specifiers in the function header let functions return other data types.

Calling function

• A function can be called by using its name in a statement.

Categories of functions

• Functions can be categorized by whether they take arguments, whether they return values.
• Different types have different roles in programming.

Parameter Passing Techniques

• Call by Value: The process of passing the actual value of variables; the function receives a copy not the original.
• Call by Reference: The function receives the address of the variable; changes made inside the function affect the original variable.