Prime Number:

  A prime number is a number that divided by self or 1 and no other number can divide that is called a prime number. 1 is not a prime number because there is must be divided by two number that are 1 and that number.

Ex-      2,3,5,7,11,13,17… etc.

Program:

using System;					

public class Program

{

 public static void Main()

 {

 int num,I;

 int temp=0;

 Console.WriteLine(“Enter a number to check whether prime or not);

 num=int.Parse(Console.ReadLine());

  for(i=2;i<=num/2;i++)

  {

   if(num%i==0)

   {

    temp=temp+1;

   }

  }

  if(temp==0)

  {

  Console.WriteLine('is Prime');

  }else

  {

  Console.WriteLine('not prime');

  }

 }

}

 Output:

 Enter a number to check whether prime or not      7

7 is prime

Print all prime number between 1 to 100.

Program:

using System;					

public class Program

{

 public static void Main()

 {	

 int num,i,j;

  int temp=0, res;

  for(num=2;num<=100;num++)

  {

  for(i=2;i<=num/2;i++)

  {

   if(num%i==0)

   {

    temp=temp+1;

   }

  }

   if(temp==0)

      {

    Console.Write(' '+num);

   }else

   {

    temp=0;

   }			

 }		

 }

}	

Output:

  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