how to compare a lowercase letter in c++ 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: check if character in string is uppercase c++

if (isupper(str[i])) {
	// str[i] is uppercase
}