Prime or not

Write a program to determine whether an integer is prime or not. A prime number is a natural number greater than 1 that has only two positive divisors: itself and 1.

For example, the prime numbers less than 200 are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199. You can use them as test cases for your program.

Remember, you should not only tests whether primes are detected correctly. You should also test other numbers and check your program says they are not prime. Also try with negative numbers.

Insist that the students test their programs by giving them ideas or
pointers about the test data to use.