How to Convert std::string to Lower Case?

Last Updated : 04 Nov, 2024

Converting string to lower case means all the alphabets present in the string should be in lower case. In this article, we will learn how to convert the std::string to lowercase in C++.

Examples

Input: s = "GEEKS for GEEKS"
Output: geeks for geeks
Explanation: All characters of s are converted to lowercase.
Input: s = "HelLO WoRld"
Output: hello world
Explanation: All characters of s are converted to lowercase.

Following are the 3 different methods to convert the std::string (C++ Style Strings) to lower case in C++:

Table of Content

Using std::transform()

We can convert the given std::string to lower case using std::transform() with std::tolower() method. This method applies the given tolower() function to each of the character converting it to lowercase if its not.

Syntax

std::transform(s.begin(), s.end(), s.begin(), ::tolower);

where, s is the string to be converted.

Example

C++

// C++ Program to convert the std::string to // lower case using std::transform() #include <bits/stdc++.h> using namespace std;  int main() {     string s = "GEEKS for GEEKS";      // Converting the std::string to lower case     // using std::transform()     transform(s.begin(), s.end(), s.begin(),               ::tolower);      cout << s;     return 0; }

Output

geeks for geeks

Time Complexity: O(n), where n is the length of string.
Auxiliary Space: O(1)

Using std::for_each()

We can also convert the given std::string to lower case using std::for_each loop with lambda function that convert the given character to its lower case using tolower() function.

Example

C++

// C++ Program to convert the std::string to // lower case using std::for_each loop with // lambda expression #include <bits/stdc++.h> using namespace std;  int main() {     string s = "GEEKS for GEEKS";      // Converting the std::string to lower case     for_each(s.begin(), s.end(), [](char& c) {         c = tolower(c);     });      cout << s;     return 0; }

Output

geeks for geeks

Time Complexity: O(n), where n is the length of string.
Auxiliary Space: O(1)

Manually Using ASCII Values

C++ uses ASCII charset in which characters are represented by 7-bit numbers called ASCII numbers. Also, lowercase alphabet for corresponding uppercase alphabet always differs by 32. So, we can use this property to convert each character of std::string to lowercase one by one by adding 32 to the uppercase character.

Example

C++

// C++ program to convert std::string to lowercase // manually using ASCII values #include <bits/stdc++.h> using namespace std;  void toLowerCase(string& s) {      	// Manual converting each character to lowercase   	// using ASCII values     for (char &c : s) {         if (c >= 'A' && c <= 'Z') {                      	// Convert uppercase to lowercase           	// by adding 32             c += 32;         }     } }     int main() {     string s = "GEEKS for GEEKS";      	// Converting s to lowercase   	toLowerCase(s);      cout << s;     return 0; }