C program to print the string in reverse order

May 27, 2022

Reverse a string in C

Today in this article we will learn how to reverse a string in C language. There are various method top reverse a sting that we will be discussing in this page.

Reversing a string is a technique so that the 1st character becomes the last character and so on.

Lets understand this with the help of an example:- 

  • Input sting:- RITIKA
  • Output sting:- AKITIR
reverse a string

Algorithm

  • Step 1. Take the string which you have to reverse as the input variable says str.
  • Step 2:- Calculate the length of the string. The actual length of the string is one less than the number of characters in the string. Let actual length be len.
  • Step 3:- Use a for loop to iterate the string using a temporary variable to swap the elements.
  • Step 4:- Print the reversed string.
C-Program-to-Reverse-A-String

C Code :-

Method 1

Run 
#include <stdio.h>

#include <string.h>  

// function definition of the revstr() 
void revstr(char *str1) 
{ 
  // declare variable 
  int i, len, temp; 
  len = strlen(str1); // use strlen() to get the length of str string 

  // use for loop to iterate the string 
  for (i = 0; i < len/2; i++) 
  { 
  // temp variable use to temporary hold the string 
   temp = str1[i]; 
   str1[i] = str1[len - i - 1]; 
   str1[len - i - 1] = temp; 
  } 
 } 

int main() 
{ 
  char str[50]="priyanka"; // size of char string 
  pri

  printf (" \n Before reversing the string: %s \n", str); 

  // call revstr() function 
  revstr(str); 
  printf (" After reversing the string: %s", str); 
 }

Output:-

Before reversing the string: priyanka 
After reversing the string: aknayirp

Method 2

We can also do the same by using build in functions.

  • like strrev() in C programming language
  • strrev() is a built in function in C which is comes under string.h header file
  • this function returns the string after reversing it.
Run 
#include <stdio.h>

#include <string.h>
int main() 
{ 
  // declare the size of character string 
char str[100] = "Ritika"; 

// use strrev() function to reverse a string 
printf ("After the reverse of a string: %s ", strrev(str)); 
return 0;
}

Output:-

Enter a string to be reversed: Ritika
After the reverse of a string: akitiR

Method 3

We can also reverse the string by storing the reverse in another array and then print.

  • The idea is to transfer the string to another string in a reverse manner let the another array is rev.
  • All we need is the size of the string.
  • The method is to initialize a character array of the equal size and start copying the elements of the input string from the end.
  • And display the rev
Run 
#include <stdio.h>

#include <string.h>

int main() {
    char str[1000] = "Priya", rev[1000];
    int i, j, count = 0;
    printf("String Before Reverse: %s", str);
    // finding the length of the string
    while (str[count] != '\0') {
        count++;
    }
    j = count - 1;
    // reversing the string by swapping
    for (i = 0; i < count; i++) {
        rev[i] = str[j];
        j--;
    }
    printf("String After Reverse: %s", rev);
    return 0;
}

Output:-

String Before Reverse: priya
String After Reverse: ayirp

Method 4

  • This includes use of two pointers one at the starting and one at the end.
  • the characters are then reversed one by one
  • The process of reversing the string is done with the help of two pointers.
Run 
#include <stdio.h>

#include <string.h>
// function declaration str_len that  
int str_len(char *ptr) 
{ 
  int i = 0; 
  while ( *(ptr + i) != '\0') 
  i++; 
  return i; 
}
void revstr(char *st) 
{ 
  int len, i; 
  char *start, *end, temp; 
  len = str_len (st); 
  start = st; 
  end = st; 

  for (i = 0; i < len - 1; i++) 
  end++; 

  for (i = 0; i < len/2; i++) 
  { 
    temp = *end; 
    *end = *start; 
    *start = temp; 

    start++; 
    end--; 
   } 
 }

int main() 
{ 
  char st[50]="priyanka"; 
 
  revstr(st); 
  printf (" The reverse string is: %s", st); 
  return 0; 
}

Output:- 

 Enter a string to be reversed: priyanka
The reverse string is: aknayirp