int main() {
 int source_number = 65; // the number that we need to check

 int decimal_digit = source_number/10; // the deciman digit (in our case it is 6)
 int unit_digit = source_number - decimal_digit * 10; // the unit digit (in our case is 5)
 printf("Dec %d, unit %d", decimal_digit, unit_digit);
}