Java Program to Print Prime Number between 1 to 100

WAP to print all prime numbers between 1 to 100 in Java

What are Prime Numbers ?

A prime number is a natural number greater than 1 that has only two factors: 1 and itself.
Examples: 2, 3, 5, 7, 11, 13, 17, etc.
Non-prime numbers (composite): 4, 6, 8, 9, 10 (since they have more than two factors).

Logical Steps:

Iterate through numbers from 2 to 100.
For each number, check divisibility from 2 to the square root of the number.
If the number is divisible by any value in this range, it is not prime.
If no divisors are found, the number is prime.
Print all prime numbers.

Programs:

Below is the simple program:

public class PrimeNumbers1to100
{
    public static void main(String[] args)
    {
        System.out.println("Prime numbers between 1 and 100 are:");

        for (int num = 2; num <= 100; num++)  // Loop from 2 to 100
        {
            boolean isPrime = true;

            for (int i=2; i < num/2; i++)
            {
                if (num % i == 0)
                {
                    isPrime = false;
                    break;
                }
            }

            if (isPrime)  // If no divisors found, it's prime
            {
                System.out.print(num + " ");
            }
        }
    }
}

Output:

Prime numbers between 1 and 100 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

Program Explanation:

Iteration and Variables:
- The program iterates through numbers from 2 to 100.
- Uses a flag variable (isPrime) to indicate if a number is prime (true initially).
Prime Check Logic:
- For each number, a loop checks divisibility from 2 to num / 2.
- If num % i == 0, set isPrime = false and exit the loop (the number is not prime).
Display Result:
- If isPrime = true, print the number (it is a prime number).
Continue to Next Number:
- If the number is prime, move to the next iteration in the loop.

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