A number is said to be prime number if that number is greater than one and can only be divided by 1 or itself. For example, 2, 3, 5 and 7 etc are prime numbers. Here in this blog, we will see how to write a program in C# to check whether a number is prime number or not.

## Program to Check a Number is Prime Number

**Getting Started**

A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number.

For example, 5 is prime because the only ways of writing it as a product, 1 × 5 or 5 × 1, involve 5 itself. However, 4 is composite because it is a product (2 × 2) in which both numbers are smaller than 4.

Primes are central in number theory because of the fundamental theorem of arithmetic: every natural number greater than 1 is either a prime itself or can be factorized as a product of primes that is unique up to their order

### Find Prime Number From The Given Number

The below code example is written in the console application which describes how to check a given number is a prime number or not.

```
static void Main(string[] args)
{
Console.Write("Enter a Number : ");
int number = int.Parse(Console.ReadLine());
bool IsPrime = true;
for (int i = 2; i < number / 2; i++)
{
if (number % i == 0)
{
IsPrime = false;
break;
}
}
if (IsPrime)
{
Console.Write("{0} is a Prime Number.",number);
}
else
{
Console.Write("{0} is not a Prime Number.",number);
}
Console.ReadKey();
}
```

*Prime Number*

**Output-1**

```
Enter Number: 87
87 is not a Prime Number
```

**Output-2**

```
Enter Number: 57
57 is a Prime Number
```

### Find the Prime Number from the given Interval

The following code example takes two numbers a argument and find the prime numbers available between the two numbers.

```
static void Main(string[] args)
{
Console.Write("Enter the start number: ");
int number1 = int.Parse(Console.ReadLine());
Console.Write("Enter the end number: ");
int number2 = int.Parse(Console.ReadLine());
Console.WriteLine("The prime number/s of given range");
for (int i = number1; i <= number2; i++)
{
int counter = 0;
for (int j = 2; j <= i / 2; j++)
{
if (i % j == 0)
{
counter++;
break;
}
}
if (counter == 0 && i != 1)
{
Console.WriteLine(i);
}
}
Console.ReadKey();
}
```

*Prime Number*

**Output**

```
Enter the start number: 1
Enter the end number: 50
The prime number/s of given range
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
```

**Thanks**