How to Convert std::string to Lower Case?

A String is a data structure in C++ language used to store a set of characters. It can be a single word or can contain a sentence and also can contain large text. In this article, we will learn how to convert string to lowercase.

Example:

Input:
myString = "This Is Some StrIng"

Output:
myString = "this is some string"

Convert std::string to Lower Case in C++

To convert string to lowercase, we will use the function std::tolower() which converts any uppercase letter into a lowercase letter. If any lowercase letter is provided to it, the function keeps it as it is.

Approach

1. We will go at each character by iterating through a string using a loop.
2. We will then pass each character to the tolower() function which will return the lowercase of it.
3. We will then append this returned character to the new string where the lowercase version will be stored.

C++ Program to Convert std::string to Lower Case

C++

// C++ Program to Convert std::string to Lower Case
#include <cctype>
#include <iostream>
#include <string>

using namespace std;

string convertToLowercase(const string& str)
{
    string result = "";

    for (char ch : str) {
        // Convert each character to lowercase using tolower
        result += tolower(ch);
    }

    return result;
}

// Driver Code
int main()
{
    string input = "ABCDE";
    cout << " string: " << input << endl;

    string lowercase_str = convertToLowercase(input);
    cout << "String in lowercase: " << lowercase_str
         << endl;

    return 0;
}

Output

 string: ABCDE
String in lowercase: abcde

Time complexity: O(N)
Space complexity: O(N)