If number formed by last four digits is divisible by 16.
int last = str . charAt ( n - 1 ) - '0' ; int second_last = str . charAt ( n - 2 ) - '0' ; int third_last = str . charAt ( n - 3 ) - '0' ; int fourth_last = str . charAt ( n - 4 ) - '0' ; return ( ( fourth_last * 1000 + third_last * 100 + second_last * 10 + last ) % 16 == 0 ) ; }