C Program to Reverse a Sentence Using Recursion

Reversing a sentence is a common problem that can be solved using various methods in programming. Recursion offers an elegant solution to this problem by breaking it down into smaller, manageable subproblems. This article explores three different C Program to Reverse a Sentence Using Recursion, providing detailed explanations, example code, and outputs for each.

Prerequisites

Before diving into the solutions, ensure you have the following prerequisites:

• Basic understanding of C programming.
• Familiarity with functions and recursion.
• A C compiler installed on your system (e.g., GCC).

Solution 1: Simple Character-by-Character Reversal

1.1 Explanation

In this approach, we will create a recursive function that processes the sentence character by character from the end to the beginning, effectively reversing it.

1.2 Program

#include <stdio.h>

void reverseSentence() {
    char c;
    scanf("%c", &c);
    if (c != '\n') {
        reverseSentence();
        printf("%c", c);
    }
}

int main() {
    printf("Enter a sentence: ");
    reverseSentence();
    return 0;
}

1.3 Output

Enter a sentence: Hello World
dlroW olleH

Solution 2: Reversing Words in a Sentence

2.1 Explanation

This approach focuses on reversing the order of words in a sentence while maintaining the order of characters within each word. We use recursion to process each word individually.

2.2 Program

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

void reverseWords(char *str, int start, int end) {
    if (start >= end) return;
    
    int wordEnd = start;
    while (wordEnd <= end && str[wordEnd] != ' ') {
        wordEnd++;
    }

    reverseWords(str, wordEnd + 1, end);
    
    for (int i = start; i < wordEnd; i++) {
        printf("%c", str[i]);
    }
    if (wordEnd <= end) {
        printf(" ");
    }
}

int main() {
    char str[100];
    printf("Enter a sentence: ");
    fgets(str, sizeof(str), stdin);
    str[strcspn(str, "\n")] = '\0';  // Remove newline character

    reverseWords(str, 0, strlen(str) - 1);
    return 0;
}

Output

Enter a sentence: Hello World
World Hello

Solution 3: Reversing Sentence Using Pointer Manipulation

3.1 Explanation

This approach uses pointer manipulation to reverse the sentence. The recursive function swaps characters at the beginning and end of the sentence, progressively moving towards the center.

3.2 Program

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

void reverse(char *start, char *end) {
    if (start >= end) return;
    char temp = *start;
    *start = *end;
    *end = temp;
    reverse(start + 1, end - 1);
}

int main() {
    char str[100];
    printf("Enter a sentence: ");
    fgets(str, sizeof(str), stdin);
    str[strcspn(str, "\n")] = '\0';  // Remove newline character

    reverse(str, str + strlen(str) - 1);
    printf("Reversed sentence: %s\n", str);
    return 0;
}

Output

Enter a sentence: Hello World
Reversed sentence: dlroW olleH

Conclusion

Reversing a sentence using recursion in C can be accomplished through various methods, each suitable for different scenarios. The simple character-by-character reversal is straightforward and easy to understand. Reversing words in a sentence while maintaining the order of characters within each word offers a more structured approach. Using pointer manipulation to swap characters provides a more low-level, efficient solution.

By understanding these techniques, you can effectively implement recursive solutions to reverse a sentence, enhancing your ability to write clean and efficient code in C. Experiment with these approaches to deepen your understanding and improve your programming skills.