I want to print prime numbers from 2 to 100. But some error is there in the code. Can anyone point out ?

Question

1.50/5 (2 votes)

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C#

int i, j, count =0;

for (i=2; i<=100; i++)
{
    for (j=1; j<=100; j++)

    {
        if (i % j == 0)
        {
            count++;

        }
    }

    if (count == 2)
    {
        Console.WriteLine("This is a prime number" + i);
        count = 0;
    }

}

Console.ReadLine();

Posted 2-Mar-13 17:02pm

Allwin456

Updated 2-Mar-13 17:25pm

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ)

v4

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PIEBALDconsult · Accepted Answer · 2013-03-02T17:47:00

Solution 2

You only reset count if the current count is two, but you should always reset it.

And you only need to check up to the square root of the number you are checking.

And look into http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes[^]

Posted 2-Mar-13 17:47pm

PIEBALDconsult

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) · Accepted Answer · 2013-03-02T17:23:00

C#

int i, j, count =0;

 for (i=2; i<=100; i++)
 {
     for (j=1; j<=i; j++)

     {
         if (i % j == 0)
         {
             count++;
         }
     }

     if (count == 2)
     {
         Console.WriteLine("This is a prime number" + i);
     }

     // This should be after the if, as we need to make it 0 every time.
     count = 0;
 }

 Console.ReadLine();

1. You should have the second loop condition like j<=i and not j<=100.
Actually you need to check whether the number is divisible with 1, 2.... upto the number you are comparing with (that is i).

2. Count should be 0 every time, but you are making it 0 when it is prime, inside the if condition.
So, 2, 3 are prime, and when 4 comes it does not make count 0, hence stops.

Thanks...