C++ tolower() – Convert String to Lowercase

In this C++ Tutorial we will explore the tolower() function, which can be used to convert a single character to it’s lowercase version. We will proceed to show exactly how one can convert an entire C++ String to lowercase, using the tolower() function.

C++ tolower() Syntax

The C++ tolower() function takes a single parameter, which is an integer representing the ascii value of a char. Don’t worry, you can still pass datatypes of type char. They are just integers in the end after all (Remember the ASCII table).

tolower(int ch);

Example# 1 (Converting a Char)

In this example, we will take a look at how to convert some simple characters in C++ to lowercase using the tolower() function. You can pass both lowercase and uppercase characters into it.

int main() {
    char a = 'A';
    char b = 'B';
    char c = 'C';

    cout << tolower(a) << endl;
    cout << tolower(b) << endl;
    cout << tolower(c) << endl;
}

The output:

97
98
99

If you want the output to be in the form of actual characters, you can use typecasting, and convert the int value to its’ character representation.

int main() {
    char a = 'A';
    char b = 'B';
    char c = 'C';

    cout << (char) tolower(a) << endl;
    cout << (char) tolower(b) << endl;
    cout << (char) tolower(c) << endl;
}

The output:

a
b
c

Alternatively, you can just store the int value returned into a char variable, which will print out an actual character if you try printing it.

Example# 2 (Converting a String)

In this example we will take a String with Uppercase characters and convert it to a Lowercase string.

The tolower() function does not work on strings natively, but remember that a String is merely a collection of characters. Hence, with the following approach, where iterate over each individual character in a String, we can convert it to lowercase.

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


int main() {
    string var = "HELLO WORLD";

    for (int i = 0; i < var.length(); i++) {
        var[i] = tolower(var[i]);
    }

    cout << "New String: " << var << endl;
}

The output:

New String: hello world

Alternatives

There are other alternatives for converting a C++ string to Lowercase. You can find a complete C++ String to Lowercase tutorial + examples by following this link.

This marks the end of the C++ tolower(), Converting String to Lowercase Tutorial. Any suggestions or contributions for CodersLegacy are more than welcome. Questions regarding the tutorial content will be asked in the comments section below.