Question

C programming 3.23 LAB: Interstate highway numbers

Primary U.S. interstate highways are numbered 1-99. Odd numbers (like the 5 or 95) go north/south, and evens (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. Note: 200 is not a valid auxiliary highway because 00 is not a valid primary highway number.

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.

Ex: If the input is:

90
the output is:

I-90 is primary, going east/west.

Answer 1

To determine if a U.S. interstate highway number is primary or auxiliary and its direction, check the number range and whether it's odd or even. Primary highways are numbered 1-99 with odd numbers running north/south and even numbers running east/west. Auxiliary highways are numbered 100-999 and service the primary highway indicated by their last two digits.

Step-by-step explanation:

To determine if a U.S. interstate highway number refers to a primary or auxiliary highway and its direction, we can use the value of the highway number. If the highway number is between 1 and 99, it is a primary highway. If it is odd, it runs north/south; if it's even, it runs east/west. On the other hand, if the highway number is within the range of 100 to 999, it is an auxiliary highway, and the rightmost two digits indicate the primary highway it services. However, we need to remember that the primary highway number must be between 1 and 99, so anything like "00" is not valid.

Here's a step-by-step example to clarify:

• 
  
• If the input is 90, check if it's less than 100. Since it is, we determine it's a primary highway.
• 
  
• Since 90 is an even number, it means the highway goes east/west.

Therefore, the output would be: I-90 is primary, going east/west.