tolower() Function in C++

The tolower() function in C++ is used to convert an uppercase alphabet character into its lowercase equivalent. It is a predefined function available in the <cctype> header file.

• It converts uppercase characters (A-Z) into lowercase characters (a-z).
• Lowercase letters, digits, and special symbols remain unchanged.

Example: Convert Single Character to Lowercase

#include <iostream>
using namespace std;

int main()
{

    char c = 'G';

    cout << c << " in lowercase is represented as = ";

    // tolower() returns an int value there for typecasting
    // with char is required
    cout << (char)tolower(c);
}

G in lowercase is represented as = g

Syntax

int tolower(int ch);

Parameter:

• ch: Character to be converted into lowercase

Return Value:

• The function returns the ASCII value of the lowercase character corresponding to the given character.

Header File:

#include <cctype>

Example: Convert String to Lowercase

#include <bits/stdc++.h>
using namespace std;

int main()
{

    // string to be converted to lowercase
    string s = "GEEKSFORGEEKS";
  
    for (auto& x : s) {
        x = tolower(x);
    }
  
    cout << s;
    return 0;
}

geeksforgeeks

Note:  If the character passed in the tolower() is any of these three

1. lowercase character
2. special symbol
3. digit

tolower() will return the character as it is.

Example: Lowercase Conversion with Digits and Symbols

#include <iostream>
using namespace std;

int main() {

    string s="Geeks@123";
  
      for(auto x:s){
      
          cout << (char)tolower(x);
    }
  
    return 0;
}