Mass lowercaser for C char[] strings

// <3 <3 <3
#define IS_INRANGE(num, a, b) ((a-1<num)&&(num<b+1))

void toLowerCase (char * string, int size) {
    int temp;
    for (int i = 0; i < size; ++i)
    {
        temp = string[i];
        if (IS_INRANGE(temp, 65, 90))
            string[i] = temp+32;
    }
}