Q:

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

belongs to collection: C# Basic Programs | Looping programs

mahmoud2506
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2022-05-09
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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.

 

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mahmoud2506
2022-05-09
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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.

 

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