how to convert uppercase character in 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: c++ char to uppercase

char choice; 
// it will instantly transform it to upper case without the need
// to convert it to int first
choice = (char)toupper(choice);