1. Working with a Function

a. Define Function

A function is a block of code that performs a specific task. In C, functions help modularize programs and make code reusable and easier to maintain.

b. Syntax of Functions

return_type function_name(parameters)
{
    // body of the function
}
      

c. Types of Functions

• Library Functions: Predefined functions provided by C libraries (e.g., printf(), scanf()).
• User Defined Functions: Functions created by the programmer to perform custom tasks.

d. Components of Function

• Function Prototype: Declaration of a function before its use.
• Function Call: Statement that invokes the function.
• Function Definition: Body of the function where actual statements are written.
• Return Type: Data type of value returned by the function.

2. Categories of Function with Examples

i. Function with Return Type but No Arguments

int getNumber()
{
    return 10;
}
      

ii. Function with Return Type with Arguments

int add(int a, int b)
{
    return a + b;
}
      

iii. Function with No Return Type and No Arguments

void display()
{
    printf("Hello World");
}
      

iv. Function with No Return Type but with Arguments

void printNumber(int n)
{
    printf("Number is %d", n);
}
      

3. Storage Classes

• Automatic: Default storage class for local variables.

  
      void demo()
      {
          int x = 10; // automatic by default
          printf("%d", x);
      }
          

• External: Variables declared outside all functions and accessible globally.

  
      #include <stdio.h>
  
      int globalVar = 5; // external
  
      void show()
      {
          printf("%d", globalVar);
      }
          

• Register: Variables stored in CPU registers for faster access.

  
      void fastAccess()
      {
          register int i;
          for(i = 0; i < 10; i++)
              printf("%d ", i);
      }
          

• Static: Variables that retain their value between function calls.

  
      void counter()
      {
          static int count = 0;
          count++;
          printf("Count = %d\n", count);
      }
          

4. Recursive Function with Syntax and Example

A recursive function calls itself to solve smaller subproblems.

Syntax:

return_type function_name(parameters)
{
    if(condition)
        return result;
    else
        return function_name(updated_parameters);
}
      

Example 1: Factorial

#include <stdio.h>
int fact(int);
int main()
{
    int n;
    printf("Enter a number: ");
    scanf("%d", &n);
    printf("Factorial of %d is %d\n", n, fact(n));
    return 0;
}

int fact(int n)
{
    if(n == 0 || n == 1)
        return 1;
    else
        return n * fact(n - 1);
}
      

Output:

Example 2: Sum of natural numbers

#include <stdio.h>
int sum(int);
int main()
{
    int n;
    printf("Enter a number: ");
    scanf("%d", &n);
    printf("Sum of first %d natural numbers is %d\n", n, sum(n));
    return 0;
}

int sum(int n)
{
    if(n == 0)
        return 0;
    else
        return n + sum(n - 1);
}
      

Output:

5. Passing Array to a Function

Example: Sum of Array Elements

#include <stdio.h>
void addarray(int[], int);
int main() 
{
    int n;
    printf("Enter the number of elements in the array: ");
    scanf("%d", &n);
    
    int arr[n];
    printf("Enter %d elements:\n", n);
    for(int i = 0; i < n; i++) 
    {
        scanf("%d", &arr[i]);
    }
    addarray(arr, n); 
    return 0;
}

void addarray(int arr[], int size) 
{
    int sum = 0;
    for(int i = 0; i < size; i++) 
    {
        sum += arr[i];
    }
    printf("Sum of the array elements is: %d\n", sum);
}
      

Output: