Reverse a String in C/C++

There can be multiple ways to reverse a string in C and C++. In this article, we will learn reversing a string using different approaches with the appropriate examples.

Consider the below example with input and output scenarios:

Input
// characters representation from left to right
inp = "Tutorialspoint"

Output
// characters representation from right to left
out = tniopslairotuT

Now, we have following approaches to solve the reverse of a given approach:

• Using Two Pointer
• Using reverse() Function
• Using strlen() Function

Reverse String Using Two Pointer

Two-pointer is one of the best technique to reverse the given string. It initializes the pointer at the left in the start and right in the end. Then use logic of swapping and assign increment and decrement operator to solve the process of reverse characters.

Example

In this example, we use two-pointer technique that result the string characters from right to left:

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

// function to reverse a string in place
void revString(char *str) {
   // Pointer intialization for left and right side characters
   int left = 0, right = strlen(str) - 1;  
    
   // loop until left pointer crosses right pointer
   while (left < right) {
       char temp = str[left];  
       str[left] = str[right]; 
       str[right] = temp;     
       left++;  
       right--; 
   }
}

int main() {
   char str[] = "Tutorialspoint";  
   revString(str);    
    
   printf("Reversed String: %s\n", str);  
   return 0; 
}

Reversed String: tniopslairotuT

#include <iostream>
#include <cstring>

using namespace std;

// function to reverse a string in place
void revString(char *str) {
   int left = 0, right = strlen(str) - 1;

   while (left < right) {
       char temp = str[left];
       str[left] = str[right];
       str[right] = temp;
       left++;
       right--;
   }
}

int main() {
   char str[] = "Tutorialspoint";
   revString(str);

   cout << "Reversed String: " << str << endl;
    
   return 0;
}

Reversed String: tniopslairotuT

Reverse String Using reverse() Function

You can also use the reverse() function, it is an in-built of the header <algorithm>. To reverse a string using reverse(), you need to pass two iterators as arguments: begin() and end(), where the begin() iterator points to the first character of the string and the end() iterator points just past the last character.

Demonstration of begin() and end() in the characters form.

Initial string : "Hello"

Swap the characters:

'H' > 'o' > "oellH"
'e' > 'l' > "olleH"
...

Example

Following is the basic example of reverse() function to solve the reverse of a string:

#include<iostream>
#include<algorithm>
#include<string>

using namespace std;

int main() {
   string str = "Tutorix";   
   reverse(str.begin(), str.end());  
   
   // display the result   
   cout << "Reversed String: " << str << endl;
   return 0;
}

Output

The above program produces the following result:

Reversed String: xirotuT

Reverse String Using strlen() Function

Another simple approach is to iterate over the characters of the string using the stelen() function and loop. In this approach, we simply get the index of the last character using the strlen(str) - 1 and then run the loop from this index to 0.

Example

In this example, use the strlen() function to show the usage of reverse string:

#include <iostream>
#include <cstring>
using namespace std;

int main() {
   char str[] = "samsung";
   cout << "Original string: " << str;

   cout << endl << "String after reverse: ";
   for (int i = strlen(str) - 1; i >= 0; i--) {
      
	  // diplay the reverse characters
      cout << str[i];  
   }

   return 0;
}

Output

The above program produces the following result:

gnusmas