## Friday, 25 May 2012

### C# program to print prime numbers

A prime number is not divisible by any other number apart from 1 and itself. So, we use this logic in this program to determine if a number is prime.

using System;

namespace SamplePrograms
{
{
public static void Main()
{
// Declare a boolean variable to determine is if a number is prime
bool isNumberComposite = false;
int j;

// Prompt the user to enter their target number

// Read the target number and convert to integer
int target = Int32.Parse(Console.ReadLine());

// 1 is neither prime nor composite. So start at 2
for (int i = 2; i <= target; i++)
{
for (j = 2; j < i; j++)
{
// A number is not prime if it is divisible by any other number,
// other than 1 and itself.

if (i % j == 0)
{
isNumberComposite = true;
// We can break out of the inner for loop as we know the number
// is not prime

break;
}
}
// Print the number if it is not composite
if (!isNumberComposite)
Console.Write("{0} ", j);
else
isNumberComposite = false;
}

// This line is to make the program wait for user input,
// instead of immediately closing