how to switch lowercase letter to upper cpp code example

Example 1: how to compare lower case character to uppercase cpp

for(int i=0;i<str.size();i++){
int c = str[i]; 
        if (islower(c))  
            str[i] = toupper(c);
}

Example 2: convert all characters in string to uppercase c++

transform(str.begin(), str.end(), str.begin(), ::toupper);