C Program to Reverse a String

Introduction

Reversing a string involves changing the order of characters in the string so that the last character becomes the first, the second-to-last becomes the second, and so on. This guide will show you how to write a C program to reverse a string provided by the user.

Problem Statement

Create a C program that:

• Takes a string as input from the user.
• Reverses the string.
• Displays the reversed string.

Example:

• Input: String = "Hello"
• Output: Reversed String = "olleH"

Solution Steps

1. Include the Standard Input-Output and String Libraries: Use #include <stdio.h> for standard input-output functions and #include <string.h> for string functions.
2. Write the Main Function: Define the main function, which is the entry point of every C program.
3. Declare Variables: Declare variables to store the string, its length, and a temporary variable for swapping characters.
4. Input the String: Use scanf or gets to take input from the user for the string.
5. Reverse the String: Use a loop to reverse the string by swapping characters from the beginning and the end.
6. Display the Reversed String: Use printf to display the reversed string.

C Program

#include <stdio.h>
#include <string.h>

int main() {
    // Step 1: Declare variables to hold the string, its length, and a temporary variable for swapping
    char str[100];
    int length, i;
    char temp;

    // Step 2: Prompt the user to enter a string
    printf("Enter a string: ");
    gets(str);  // Using gets to read the string including spaces

    // Step 3: Find the length of the string
    length = strlen(str);

    // Step 4: Reverse the string by swapping characters
    for (i = 0; i < length / 2; i++) {
        temp = str[i];
        str[i] = str[length - 1 - i];
        str[length - 1 - i] = temp;
    }

    // Step 5: Display the reversed string
    printf("Reversed string: %s\n", str);

    return 0;  // Step 6: Return 0 to indicate successful execution
}

Explanation

Step 1: Declare Variables

• The variable str is declared to store the input string. The variable length is used to store the length of the string, and i is used as a loop counter. temp is used as a temporary variable for swapping characters.

Step 2: Input the String

• The program prompts the user to enter a string using printf. The gets function is used to read the string, allowing it to include spaces.

Step 3: Find the Length of the String

• The strlen function from the string.h library is used to calculate the length of the string.

Step 4: Reverse the String

• The program uses a for loop to iterate over the string:
  • Characters from the beginning of the string are swapped with characters from the end using the temp variable.
  • The loop continues until it reaches the middle of the string.

Step 5: Display the Reversed String

• After the string is reversed, the program displays the reversed string using the printf function.

Step 6: Return 0

• The return 0; statement indicates that the program executed successfully.

Output Example

Example 1:

Enter a string: Hello
Reversed string: olleH

Example 2:

Enter a string: C Programming
Reversed string: gnimmargorP C

Conclusion

This C program demonstrates how to reverse a string by swapping characters from the beginning and end of the string. It covers basic concepts such as string manipulation, loops, and conditional statements, making it a useful example for beginners learning C programming.