C# Prime Number - c# - c# tutorial - c# net



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How to write Prime number Program in C# ?

  • Prime number is a number that is greater than 1 and divided by 1 or itself.
  • In other words, prime numbers can't be divided by other numbers than itself or 1.
  • For example- 2, 3, 5, 7, 11, 13, 17, 19, 23.... are the prime numbers.
  • Let's see the prime number program in C#.
  • In this C# program, we will take an input from the user and check whether the number is prime or not.
 C# Prime Number

C# Prime Number

Example1:

using System;  
public class PrimeNumberExample  
{  
public static void Main(string[] args)  
{  
int n, i, m=0, flag=0;    
Console.Write("Enter the Number to check Prime: ");    
n = int.Parse(Console.ReadLine());  
m=n/2;    
for(i = 2; i <= m; i++)    
{    
if(n % i == 0)    
{    
Console.Write("Number is not Prime.");    
flag=1;    
break;    
}    
}    
if (flag==0)    
Console.Write("Number is Prime.");       
}  
}  

C# examples - Output :

Enter the Number to check Prime: 17  
Number is Prime.   
Enter the Number to check Prime: 57  
Number is not Prime.

Example2:

/*
C# Program to Check Whether the Given Number is a Prime number if so then 
Display its Largest Factor
*/
using System;
namespace example
{
class prime
{
public static void Main()
{
Console.Write("Enter a Number: ");
int num;
num = Convert.ToInt32(Console.ReadLine());
int k;
k = 0;
for (int i = 1; i <= num/2; i++)
{
if (num % i == 0)
{
k++;
}
}
if (k == 2)
{
Console.WriteLine("Entered Number is a Prime Number and the Largest Factor is {0}",num);
}
else
{
Console.WriteLine("Not a Prime Number");
}
Console.ReadLine();
}
}
}

output:

Enter a Number: 11
Entered Number is a Prime Number and the Largest Factor is 11


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