Exercise 2-10

Rewrite the function lower, which converts upper case letters to lower case, with a conditional expression instead of if-else.
Noting that 
    if (condition)
        do x;
    else
        do y;
looks like (condition) ? do x : do y; when written using a conditional expression, lower reads as follows: 
    /* lower:  convert c to lower case; ASCII only */
    int lower(int c)
    {
        if (c >= 'A' && c <= 'Z')
            return c + 'a' - 'A';
        else
            return c;
        return (c >= 'A' && c <= 'Z') ? c + 'a' - 'A' : c;
    }

The syntax may seem cryptic, especially if this is your first time seeing it, so try using conditional expressions in previous exercises where possible in order to become more comfortable with them.