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C program to swap adjacent characters of a string

In this C program, we are going to learn how to swap adjacent characters of a string? Here, we will have a string with even number of characters (string length must be even to swap the adjacent characters).
Submitted by IncludeHelp, on April 05, 2018

Problem statement

Given a string and we have to swap its adjacent characters using C program.

Swapping adjacent characters of a string

Here, to swap adjacent characters of a given string - we have a condition, which is "string length must be EVEN i.e. string must contains even number of characters".

Example

Input:
String: "help"
Output:
String: "ehpl"

Input:
String: "Hello"
Output:
The length of the string is Odd..

Program to swap adjacent characters of a string in C

/** C program to swap adjacent characters
 * of a string but obly if it is of even
 * length
 */

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

// main function
int main() {
  // Declare an integer pointer
  char string[30] = {0};
  char c = 0;
  int length = 0, i = 0;

  // Take string input from the user
  printf("\nEnter the string : ");
  fgets(string, 30, stdin);  // gets(string);

  // calculate the length of the string
  length = strlen(string);

  if (length % 2 == 0) {
    for (i = 0; i < length; i += 2) {
      c = string[i];
      string[i] = string[i + 1];
      string[i + 1] = c;
    }
    printf("\nAfter Swap String : %s", string);
  } else {
    printf("\nThe length of the string is Odd..\n");
  }

  return 0;
}

Output

Run 1: 
Enter the string : help
After Swap String : ehpl

Run 2:
Enter the string : program
The length of the string is Odd..

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