C Exercises: Reverse a string partially

Last update on March 19 2025 12:32:53 (UTC/GMT +8 hours)

2. Reverse Substring

Write a C program that takes a string and two integers (n1, n2). Now reverse the sequence of characters in the string between n1 and n2.
Let l be the length of the string.

Constraints:

• 1 ≤ n1 ≤ n2 ≤ l ≤100
• Each letter of the string is an uppercase or lowercase letter.

Sample Date:

("abcdxyabcd", 5, 6) -> "abcdyxabcd"
("Exercises", 1, 3) -> "exercises"

C Code:

#include <stdio.h> // Include standard input/output library
#include <string.h> // Include string handling library

int main(void)
{
char text[101] = {0}; // Declare an array 'text' to hold the input string
char result[101] = {0}; // Declare an array 'result' to hold the modified string
int n1, n2, l; // Declare variables for position inputs and string length

    // Prompt the user to input a string
printf("Input a string: ");

    // Read the input string from the user and store it in the 'text' array
scanf("%s", text);

    // Prompt the user to input position-1 for reversing the string
printf("Input position-1 for reverse the string: ");

    // Read the position-1 input from the user and store it in 'n1'
scanf("%d", &n1);

    // Prompt the user to input position-2 for reversing the string
printf("\nInput position-2 for reverse the string: ");

    // Read the position-2 input from the user and store it in 'n2'
scanf("%d", &n2);

    l = strlen(text); // Calculate the length of the input string and store it in 'l'
int i = 0;

    // Copy characters from the start of 'text' to 'result' until position-1
for(; i< n1-1; i++) {
result[i] = text[i];
    }

    // Reverse and copy characters from position-2 to position-1 in 'text' to 'result'
for(int j = n2-1; i< n2; i++, j--) {
result[i] = text[j];
    }

    // Copy the remaining characters from 'text' to 'result'
for(; i<= l; i++) {
result[i] = text[i];
    }

    // Print the modified string
printf("Reverse string (partly): %s\n", result);

return 0;
}

Output:

Input a string: Input position-1 for reverse the string: abcdxyabcd 5 6
Input position-2 for reverse the string: Reverse string (partly): abcdyxabcd

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to reverse a substring between two indices of a given string without using library functions.
• Write a C program that uses pointer arithmetic to reverse the portion of a string delimited by two user-supplied indices.
• Write a C program to swap the characters between two positions in a string so that the segment is reversed in place.
• Write a C program to reverse a substring and then check if the modified string forms a palindrome.

C Programming Code Editor:

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