What are the different methods for reversing a string in C/C++?

Different Methods to Reverse a String in C/C++

What are the different methods for reversing a string in C/C++? Switching a string alludes to the procedure on a string, by which the grouping of characters in it gets turned around. For instance, consider ‘str’ contains a string “JournalDev” in it. After the inversion activity happens on the string ‘str’, the substance ought to get switched. Thus now, ‘str’ ought to contain the string “veDlanruoJ”. Presently let us perceive how we can play out this opposite procedure on C++ strings utilizing different strategies.

Switching a string alludes to the procedure on a string, by which the grouping of characters in it gets turned around. For instance, consider ‘str’ contains a string “JournalDev” in it. After the inversion activity happens on the string ‘str’, the substance ought to get switched. Thus now, ‘str’ ought to contain the string “veDlanruoJ”. Presently let us perceive how we can play out this opposite procedure on C++ strings utilizing different strategies.

Table of Contents

Example

User-defined reverse() function −

#include <bits/stdc++.h>
using namespace std;
//function to reverse given string
void reverse_str(string& str){
   int n = str.length();
   for (int i = 0; i < n / 2; i++)
      swap(str[i], str[n - i - 1]);
}
int main(){
   string str = "tutorialspoint";
   reverse_str(str);
   cout << str;
   return 0;
}

Using in-built reverse() function −

#include <bits/stdc++.h>
using namespace std;
int main(){
   string str = "tutorialspoint";
   reverse(str.begin(), str.end());
   cout << str;
   return 0;
}

Printing reverse of a given string−

#include <bits/stdc++.h>
using namespace std;
void reverse(string str){
   for (int i=str.length()-1; i>=0; i--)
      cout << str[i];
}
int main(void){
   string s = "tutorialspoint";
   reverse(s);
   return (0);
}

Output

eevibes

Different Methods to Reverse a String in C/C++

1- Using reverse()

reverse() method available in the algorithm header file can reverse a string in-place without writing any boilerplate code.

All we need to do is to pass the beginning and end iterator as arguments to the particular method.

Here is an example in C++, demonstrating the same:

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

int main() {
    string str = "Hello world!";
    reverse(str.begin(), str.end());
    cout << str;
    return 0;
}

Output:

!dlrow olleH

2- Using Loop

We can also reverse a string using ‘for’ or ‘while’ loop without any built-in funtion.

The idea is to iterate through the characters of the input string in reverse order and concatenate them to a new string.

To do this, we have to follow the following steps:

Input a string.
for loop from str.length() to 0 in decrementing order.
1. Concatenate each character to the reverse string i.e., rev = rev + str[i].
Output the reverse string.

Here is the implementation of the steps in C++:

#include <iostream>
using namespace std;
 
int main()
{   
    //Input string
    string str = "code";
    
    //Initialize reverse with null string value
    string rev = "";
    
    //Iterate input string in revrese order
    for(int i=str.length()-1; i>=0; i--){
        //concatenate characters to the reverse
        rev = rev + str[i];  
    }
    
    cout << rev;
    return 0;
}

Output:

edoc

3- Using Recusion

We can also reverse a string using recursion in C++. The idea is to extract the characters on each recursive call and reassign them to the string in reverse order during the traceback process.

Here is the implementation of the idea in C++:

#include <iostream>
using namespace std;

//recursive function
void reverse(string &str, int i){
    //Base condition - when index exceeds string length
    if(i == str.length())
        return;
    
    //extract character
    char ch = str[i];
    //recusively call for next character
    reverse(str, i+1);
    //reassign in reverse order
    str[str.length()-i-1] = ch;
}
 
int main()
{   
    //Input string
    string str = "Pencil Programmer";
    
    //start recirsive funtion from first index
    reverse(str, 0);
    
    //output the string
    cout << str;
    return 0;
}