Primary U. S. interstate highways are numbered 1-99. Odd numbers (like the 5 or 95) go north/south, and events (like the 10 or 90) go east/west. Auxiliary highways are numbered 100-999, and service the primary highway indicated by the rightmost two digits. Thus, I-405 services I-5, and I-290 services I-90. Given a highway number, indicate whether it is a primary or auxiliary highway. If auxiliary, indicate what primary highway it serves. Also indicate if the (primary) highway runs north/south or east/west.

The C code for the problem is given below

Explanation:

#include <stdio.h>

int main() {

   int highwayNumber;

   int primaryNumber;

   scanf("%d", &highwayNumber);

   if (highwayNumber >= 1 && highwayNumber <= 999) {

       if (highwayNumber <= 99) {

           if (highwayNumber % 2 == 0) {

               printf("I-%d is primary, going east/west.\n", highwayNumber);

           } else {

               printf("I-%d is primary, going north/south.\n", highwayNumber);

           }

       } else {

           primaryNumber = highwayNumber;

           highwayNumber %= 100;

           if (highwayNumber % 2 == 0) {

               printf("I-%d is auxiliary, serving the I-%d, going east/west.\n", primaryNumber, highwayNumber);

           } else {

               printf("I-%d is auxiliary, serving the I-%d, going north/south.\n", primaryNumber, highwayNumber);

           }

       }

   } else {

       printf("%d is not a valid interstate highway number.\n", highwayNumber);

   }

   return 0;

}