How do you reverse a string in place in C or C++?

In this section we will see how to reverse a string in place. So we will not use some other memory spaces for reversing. In C++, we can use the std::string. But for C we have to use the character array. In this program we are using the character array to take the string. Then reversing it.

Input: A string “This is a string”
Output: The reversed string “gnirts a si sihT”

Algorithm

reverse_string(str)

Input − The string

Output − The reversed string.

len := the length of the string
i := 0 and j := (len-1)
while i < j, do
   swap the characters from position i and j
   i := i + 1
   j := j - 1
done

Example Code

 Live Demo

#include <iostream>
#include<cstring>
using namespace std;
void reverse(char s[]) {
   int len = strlen(s) ; //get the length of the string
   int i, j;
   for (i = 0, j = len - 1; i < j; i++, j--) {
      swap(s[i], s[j]);
   }
}
int main() {
   char s[20] = "This is a string";
   cout << "Main String: " << s <<endl;
   reverse(s);
   cout << "Reversed String: " << s <<endl;
}

Output

Main String: This is a string
Reversed String: gnirts a si sihT