using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace PrimeNumber
{
class Math
{
static void Main(string[] args)
{
Console.WriteLine("Enter a Number : ");
try
{
int num = int.Parse(Console.ReadLine());
if (num == 2 || num == 3 || num == 5 || num == 7)
{
Console.WriteLine("Entered number is Prime number");
}
else if (num % 2 != 0 && num % 3 != 0 && num % 5 != 0 && num % 7 != 0)
{
Console.WriteLine("Entered number is prime number");
}
else
{
Console.WriteLine("Entered number is not prime");
}
}
catch(Exception ee)
{
Console.WriteLine("Exception Raised Please Enter the valid number",ee);
}
Console.ReadLine();
}
}
}
VulpesPosted Dec 16, 2014, 3:32 PM
For example, if you enter 121, you'll be informed it's a prime number when, of course, it isn't.
Here's a version I wrote some time ago which does work OK:
using System;
class Program
{
static void Main()
{
int n ;
while(true)
{
Console.Write("Enter a positive integer or 0 to finish : ");
int.TryParse(Console.ReadLine(), out n);
if (n == 0) return;
if(IsPrime(n))
{
Console.WriteLine("{0} is prime", n);
}
else
{
Console.WriteLine("{0} is not prime", n);
}
Console.WriteLine();
}
}
static bool IsPrime(int x)
{
if (x <= 1) return false;
for (int i = 2; i <= x / 2; i++)
{
if ((x % i) == 0)
{
return false;
}
}
return true;
}
}