# Write a C# Program to check whether a number is prime or not

How to write a C# program to find prime numbers. What is a prime number? And how to find the prime number between two numbers in C#.

At the very first let’s understand what is a prime number? Then will write the code to find prime number in C#. List of C# programs with examples.

# What is a prime number?

A number that is divisible only by itself and 1. Example: (2, 3, 5, 7, 11, 13, 17, 19). One is not a prime number according to the definition a Prime number is divisible with 1 and itself and one doesn’t have exactly two positive divisors.

## C# Program to check whether a number is prime or not

In this example, We will see how to check whether a number is prime or not in c#. When user will run this code It will ask to enter a number. The output will print the number is prime or not.

```using System;

namespace CSharpProgram
{
class Program
{
static void Main(string[] args)
{
int num, i, f = 0;
Console.Write("Enter any Number: ");

for (i = 2; i <= num/2; i++)
{
if (num % i == 0)
{
Console.Write("No "+num+" is not a Prime Number");
f = 1;
break;
}
}
if (f == 0) {
Console.Write("Yes " +num+ " is a Prime Number");
}

}
}
}
```

### More examples to find the prime number in C#

Below, We can see more C# program to find prime number between two numbers, for example, find a prime number between 1 to 100 in C#.

## Write a C# program to find Prime Number between 1-100

```using System;

namespace CSharpProgram
{
class Program
{
static void Main(string[] args)
{
bool isPrime = true;
Console.WriteLine("Prime Numbers between 1 to 100 : ");
for (int i = 2; i <= 100; i++)
{
for (int j = 2; j <= 100; j++)
{
if (i != j && i % j == 0)
{
isPrime = false;
break;
}

}
if (isPrime)
{
Console.Write(" " + i);
}
isPrime = true;
}
}
}
}
```

## Write a C# program to find Prime Number between n-N.

```using System;

namespace CSharpProgram
{
class Program
{
static void Main(string[] args)
{
bool isPrime = true;
Console.WriteLine("Prime Numbers between "+n1+" to "+n2+" : ");
for (int i = n1; i <= n2; i++)
{
for (int j = 2; j <= n2; j++)
{
if (i != j && i % j == 0)
{
isPrime = false;
break;
}

}
if (isPrime)
{
Console.Write(" " + i);
}
isPrime = true;
}