Pythons Project for beginners - Post 30: Prime Number Checker

Let's build a Prime Number Checker. This is a classic programming exercise that's perfect for beginners to practice with loops, conditional logic, and mathematical concepts.

First, here is the explanation of how the project is built.

How the "Prime Number Checker" is Made

1. The Core Idea: The goal is to create a program that takes a whole number from the user and determines whether it is a prime number.

2. What is a Prime Number? A prime number is a whole number greater than 1 that has only two divisors: 1 and itself. For example, 2, 3, 5, 7, and 11 are prime, while 6 is not (it's divisible by 2 and 3).

3. Getting User Input Safely: The program needs an integer to check. We'll use input() to get the number from the user and then int() to convert it to a number. This is wrapped in a try...except ValueError block to ensure the program doesn't crash if the user enters text instead of a number.

4. The Core Logic (Trial Division):

   • Handle Edge Cases: First, we check if the number is less than or equal to 1. By definition, these numbers are not prime, so we can handle this case immediately.

   • The Loop: To see if a number is prime, we need to check if it's divisible by any number other than 1 and itself. A common and efficient way to do this is to loop from 2 up to the square root of the number. If a number has a divisor larger than its square root, it must also have a corresponding divisor that is smaller.

   • The Check: Inside the loop, we use the modulo operator (%). If number % i == 0 for any number i in our loop, it means we've found a divisor.

   • Using a Flag: We'll use a boolean variable, is_prime, and set it to True initially. If we find a divisor in our loop, we change this flag to False and immediately break out of the loop, since we've proven the number is not prime and don't need to check any further.

5. Displaying the Result: After the loop is finished, we check the final state of our is_prime flag. Based on its value, we print a clear message telling the user whether their number is prime or not.