Function

 

Function

Function: A function in C is a block of code that performs a specific task and can be used many times in a program. It helps to divide a big program into small manageable parts.

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Subroutine: A subroutine is also a block of code that performs a specific task, but it does not return any value. In C, a subroutine is written using a void function.

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Uses of Function and Subroutine

Purpose	Explanation
Code Reusability	A function can be written once and used many times.
Modularity	Divides a large program into small sections (modules).
Easy Debugging	Errors can be easily found in small functions.
Improved Readability	Makes program easier to read and understand.
Teamwork	Different functions can be made by different programmers.

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Drawbacks of Functions and Subroutines

Drawback	Explanation
Extra Memory Use	Function calls require memory for parameters and return values.
Execution Overhead	Jumping in and out of functions can make the program slightly slower.
Complexity	Too many small functions can make code hard to track.

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Declaration and Initialization

(a) Function Declaration

Also called Function Prototype — it tells the compiler about the function name, return type, and parameters.

Syntax:

return_type function_name(parameter_list);

📘 Example:

int add(int, int);

void greet();

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Function Definition

Defines what the function will do.

Syntax:

return_type function_name(parameter_list) {

    // statements

}

Example:

int add(int a, int b) {

    return a + b;

}

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Function Call

Used to execute a function.

📘 Syntax:

function_name(arguments);

Example:

sum = add(5, 10);

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  Types of Functions and Subroutines

1. Library Function

Definition:
Library functions are predefined functions that are already written and stored in C header files (like stdio.h, math.h, string.h, etc.). You can use them directly in your program without writing their code.

 Examples:

printf();    // for output

scanf();     // for input

sqrt();      // for square root

strlen();    // for length of a string

Note:
To use a library function, you must include the proper header file at the beginning of your program.
Example:

#include <math.h>

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 2. User-Defined Function

Definition:
A user-defined function is a function created by the programmer to perform a specific task. It helps to make the program modular, reusable, and easy to understand.

 Example:

int add(int a, int b) {

    return a + b;

}

 Note:
User-defined functions are written by the user using the syntax:

return_type function_name(parameter_list) {

    // statements

}

 

 

Types of Functions in C (Based on Arguments and Return Value)

 1. No Arguments and No Return Value

Definition:
This type of function does not take any input (arguments) and does not return any value.
It simply performs a task like displaying a message.

Example:

#include <stdio.h>

void greet() {

    printf("Hello Students!\n");

}

int main() {

    greet();   // function call

    return 0;

}

Use:
When you only want to perform an action, not calculations.

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2. Arguments but No Return Value

Definition:
This type of function takes input values (arguments) but does not return any result to the calling function.

Example:

#include <stdio.h>

void displaySum(int a, int b) {

    printf("Sum = %d\n", a + b);

}

int main() {

    displaySum(10, 20);  // function call with arguments

    return 0;

}

Use:
When you need to process or display results directly inside the function.

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3. No Arguments but Returns a Value

Definition:
This function does not take any input, but it returns a value to the main program.

 Example:

#include <stdio.h>

int getNumber() {

    return 100;

}

int main() {

    int num = getNumber();  // function call

    printf("Number = %d", num);

    return 0;

}

Use:
When the function itself generates or calculates a value internally.

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4. With Arguments and Return Value

Definition:
This type of function takes input values (arguments) and also returns a result to the calling function.
It is the most commonly used type of function.

Example:

#include <stdio.h>

int add(int a, int b) {

    return a + b;

}

int main() {

    int sum = add(10, 20);

    printf("Sum = %d", sum);

    return 0;

}

Use:
When input is needed and output is expected.

 

 

 

                           Recursion in Function

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Recursion is a process in which a function calls itself directly or indirectly to solve a problem.

In simple words,
A recursive function is a function that calls itself.

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Syntax of Recursive Function:

return_type function_name(parameters) {

    if (condition)

        return some_value;   // Base case

    else

        return function_name(modified_parameter);  // Recursive call

}

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Important Terms:

1.     Recursive Call:
When a function calls itself, it is called a recursive call.

2.     Base Case (Termination Condition):
A condition that stops the function from calling itself again — to prevent infinite recursion.

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Example 1: Factorial Using Recursion

Program:

#include <stdio.h>

int factorial(int n) {

    if (n == 0 || n == 1)

        return 1;   // Base case

    else

        return n * factorial(n - 1);  // Recursive call

}

int main() {

    int num = 5;

    printf("Factorial of %d = %d", num, factorial(num));

    return 0;

}

 Output:

Factorial of 5 = 120

Advantages and Disadvantages of Recursion

Advantages of Recursion

No.	Advantage	Explanation
1.	Simplifies Complex Problems	Problems like factorial, Fibonacci series, and tree traversal are easier to solve using recursion.
2.	Reduces Code Length	Recursive programs are shorter and easier to write compared to long iterative loops.
3.	Better Logical Clarity	The logic of repetitive or mathematical problems becomes easier to understand.
4.	Useful for Repetitive Problems	Recursion automatically handles repetition through self-calls instead of using loops.

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🔹 Disadvantages of Recursion

No.	Disadvantage	Explanation
1.	High Memory Usage	Each recursive call uses extra stack memory, which can lead to memory overflow.
2.	Slower Execution	Calling a function repeatedly takes more time than using loops.
3.	Difficult to Debug	Tracing errors in recursive calls can be complex.
4.	Risk of Infinite Recursion	If the base condition is missing or wrong, the program never stops and crashes.