Reverse a String Using a Character Array in C

To reverse a string using a character array in C, we need to store the string in an array and swap the characters from both ends until the middle of the string is reached. This can be achieved using a loop and swapping technique or by utilizing built-in functions.

Examples to Reverse a String in C

1. Reverse a String Using a Loop

In this example, we manually reverse a string stored in a character array by swapping characters from both ends using a while loop.

main.c

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

void reverseString(char str[]) {
    int length = strlen(str);
    int start = 0, end = length - 1;
    
    // Swap characters from start and end
    while (start < end) {
        char temp = str[start];
        str[start] = str[end];
        str[end] = temp;
        
        start++;
        end--;
    }
}

int main() {
    char str[] = "hello";
    
    printf("Original String: %s\n", str);
    reverseString(str);
    printf("Reversed String: %s\n", str);

    return 0;
}

Explanation:

  1. The reverseString() function takes a character array as input.
  2. We determine the length of the string using strlen() and initialize two pointers: start at index 0 and end at the last character.
  3. Using a while loop, we swap characters from the beginning and end until they meet in the middle.
  4. After swapping, we increment start and decrement end to move towards the center.
  5. The function modifies the string in place, and we print the reversed string in the main() function.

Output:

Original String: hello
Reversed String: olleh

2. Reverse a String Using a Recursive Function

In this example, we reverse a string using recursion by swapping the first and last characters and calling the function recursively for the remaining substring.

main.c

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

void reverseRecursive(char str[], int start, int end) {
    if (start >= end)
        return;
    
    char temp = str[start];
    str[start] = str[end];
    str[end] = temp;
    
    reverseRecursive(str, start + 1, end - 1);
}

int main() {
    char str[] = "world";
    
    printf("Original String: %s\n", str);
    reverseRecursive(str, 0, strlen(str) - 1);
    printf("Reversed String: %s\n", str);

    return 0;
}

Explanation:

  1. The reverseRecursive() function swaps the first and last characters.
  2. The function is called recursively with start + 1 and end - 1 until start meets or exceeds end.
  3. When the base condition start >= end is met, the recursion stops.
  4. The main() function initializes the string and calls the recursive function with starting index 0 and last index strlen(str) - 1.

Output:

Original String: world
Reversed String: dlrow

Conclusion

In this tutorial, we explored different ways to reverse a string using a character array in C:

  1. Using a loop: Swapping characters from both ends.
  2. Using recursion: Reversing by recursively swapping characters.

Among these methods, using a loop is the most portable and widely supported approach.