how to convert string into lowercase in cpp

1  // sl is the string which is converted to lowercase 
2    string sl = "Jatin Goyal"; 
3  
4    // using transform() function and ::tolower in STL 
5    transform(sl.begin(), sl.end(), sl.begin(), ::tolower); 

1#include<bits/stdc++.h> 
2using namespace std; 
3main() { 
4    string s = "Viet Nam"; 
5    transform(s.begin(), s.end(), s.begin(), ::tolower); //lowercase
6    cout << s << endl; 
7}
8

1str[i] = tolower(str[i]);

1int i = 0;
2    while(str[i])
3    {
4        if(str[i] == std::toupper(str[i]) && std::isalpha(str[i]) == 1024)
5        str[i]+= 32;
6        ++i;
7    }