validate

Module 1

Go back to Prep for Class 2

Exercise: Validate

In a program called validate.c write a program using a do-while loop that prompts the user for an even integer. If they try to swindle you with odd numbers, just keep prompting them until you get your way:

$ ./validate
Give me an even integer please: 3
Give me an even integer please: 35
Give me an even integer please: 6
Thanks! I got what I wanted.

To determine whether a number is even, you can use the modulo operator %, which calculates the remainder after division. Here's some examples:

• 3 % 3 is 0
• 4 % 3 is 1
• 5 % 3 is 2
• 6 % 3 is 0
• 7 % 3 is 1
• ...
• 9 % 3 is 0
• 12 % 3 is 0

Notice the pattern? Whenever some number n is divisible by 3, that's equivalent to saying n / 3 has no remainder left over, so n % 3 is 0.

So to determine whether a number is even, you just need to check whether it is divisbile by 2, or in other words, whether n % 2 is 0.

If n % 2 is not equal to 0, then you have an odd number (remember how to say "not equal to" in code?).