Q:

# C# program to find out the prime numbers among 2 to 30

A number which is divisible by itself (or we can say number which is divisible by 1 and itself), note that: 1 is not a prime number, they are start from 2.

In this program, we are writing a program that will print only prime numbers from 2 to 30.

```For example:
2 is prime number.
3 is prime number.
4 is not prime number because it can be dividing by 2.
5 is again a prime number.
```

Consider the program:

``````using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{

class Program
{
static void Main(string[] args)
{
int i     = 0;
int j     = 0;
int flag  = 0;

for (i = 2; i <= 30; i++)
{
j    = 2;
flag = 0;
while(j<=(i/2))
{
if (i % j == 0)
{
flag = 1;
break;
}
j++;
}

if(flag==0)
Console.Write(i + " ");

}
Console.WriteLine();
}
}
}``````

Output

`2 3 5 7 11 13 17 19 23 29`

Here, we used a loop which is running from 2 to 30 and the inner loop is running from 2 to half of the number.

If number is divisible by any number from 2 to half of the number, it will not be a prime number and loop is breaking here.