Program to reverse words in a given string in C++

Last Updated : 30 Apr, 2020

Given a sentence in the form of string str, the task is to reverse each word of the given sentence in C++.

Examples:

Input: str = “the sky is blue”
Output: blue is sky the

Inpu: str = “I love programming”
Output: programming love I

Method 1: Using STL functions

Reverse the given string str using STL function reverse().
Iterate the reversed string and whenever a space is found reverse the word before that space using the STL function reverse().

Below is the implementation of the above approach:

// C++ program for the above approach 
  
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to reverse the given string 
string reverseString(string str) 
{ 
  
    // Reverse str using inbuilt function 
    reverse(str.begin(), str.end()); 
  
    // Add space at the end so that the 
    // last word is also reversed 
    str.insert(str.end(), ' '); 
  
    int n = str.length(); 
  
    int j = 0; 
  
    // Find spaces and reverse all words 
    // before that 
    for (int i = 0; i < n; i++) { 
  
        // If a space is encountered 
        if (str[i] == ' ') { 
            reverse(str.begin() + j, 
                    str.begin() + i); 
  
            // Update the starting index 
            // for next word to reverse 
            j = i + 1; 
        } 
    } 
  
    // Remove spaces from the end of the 
    // word that we appended 
    str.pop_back(); 
  
    // Return the reversed string 
    return str; 
} 
  
// Driver code 
int main() 
{ 
    string str = "I like this code"; 
  
    // Function call 
    string rev = reverseString(str); 
  
    // Print the reversed string 
    cout << rev; 
    return 0; 
} 

Output:

code this like I

Method 2: Without using the inbuilt function: We can create the reverse() function which is used to reverse the given string. Below are the steps:

Intially reverse each word of the given string str.
Now reverse the whole string to get the resultant string in desired order.

Below is the implementation of the above approach:

// C++ program for the above approach 
  
#include <bits/stdc++.h> 
using namespace std; 
  
// Function used to reverse a string 
// from index l to r 
void reversed(string& s, int l, int r) 
{ 
  
    while (l < r) { 
  
        // Swap characters at l and r 
        swap(s[l], s[r]); 
        l++; 
        r--; 
    } 
} 
  
// Function to reverse the given string 
string reverseString(string str) 
{ 
  
    // Add space at the end so that the 
    // last word is also reversed 
    str.insert(str.end(), ' '); 
  
    int n = str.length(); 
  
    int j = 0; 
  
    // Find spaces and reverse all words 
    // before that 
    for (int i = 0; i < n; i++) { 
  
        // If a space is encountered 
        if (str[i] == ' ') { 
  
            // Function call to our custom 
            // reverse function() 
            reversed(str, j, i - 1); 
  
            // Update the starting index 
            // for next word to reverse 
            j = i + 1; 
        } 
    } 
  
    // Remove spaces from the end of the 
    // word that we appended 
    str.pop_back(); 
  
    // Reverse the whole string 
    reversed(str, 0, str.length() - 1); 
  
    // Return the reversed string 
    return str; 
} 
  
// Driver code 
int main() 
{ 
    string str = "I like this code"; 
  
    // Function call 
    string rev = reverseString(str); 
  
    // Print the reversed string 
    cout << rev; 
    return 0; 
} 

Output:

code this like I

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.

My Personal Notes

Related Articles