Check out example codes for "tolower in c++". It will help you in understanding the concepts better.

Code Example 1

#include <cctype>
#include <iostream>
#include <cstring>
#include <cstdio>

using namespace std;

int main()
{
    char str[] = "John is from USA.";

    cout << "The lowercase version of \"" << str << "\" is " << endl;

    for (int i=0; i<strlen(str); i++)
        putchar(tolower(str[i]));
    
    return 0;
}

Code Example 2

// Include #include<bits/stdc++.h>
string s = "Jatin Goyal"; 
// using transform() function and ::tolower in STL 
transform(s.begin(), s.end(), s.begin(), ::tolower);

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