printing prime numbers sequence ??

SUNIL GUTTA

Hie

Please do check what wrong in my code i hope everything right .. but on console its just displaying one single value o/p i.e 13 .. after i press enter key its displaying next prime upon each pres .. y it is going n like this ...

using System;

using System.Collections.Generic;

using System. Linq;

using System.Text;

namespace ConsoleApplication2

{

class Program

{

static void Main()

{

for (int i = 3; i < 50;i++ )

{

if (i % 2 == 0)

continue ;

if (i % 3 == 0)

continue;

if (i % 5 == 0)

continue;

if (i % 7 == 0)

continue;

if (i % 11 == 0)

continue;

Console.WriteLine(i);

}

6 Replies

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Vulpes13y ago
Accepted answer
You don't want to continue when i = 3, 5, 7 and 11, to get a full list of prime number between 3 and 50:

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

namespace ConsoleApplication2
{
class Program
{
static void Main()

{
for (int i = 3; i < 50;i++ )
{
if (i % 2 == 0)
continue ;
if (i % 3 == 0 && i != 3)
continue;
if (i % 5 == 0 && i != 5)
continue;
if (i % 7 == 0 && i != 7)
continue;
if (i % 11 == 0 && i != 11)
continue;
Console.WriteLine(i);
}

}

}
}

The output is now:

3
5
7
11
13
17
19
23
29
31
37
41
43
47
Vulpes13y ago
Yes, that's an equivalent way of expressing the logic.

You could also express it like this and get rid of the continue:

for (int i = 3; i < 50;i++ )
{
if ((i % 2 != 0 && i % 3 != 0 && i % 5 != 0 && i % 7 != 0) || i==3 || i==5 || i==7)
Console.WriteLine(i);
}
SUNIL GUTTA13y ago
gotcha ..!!

for (int i = 3; i < 50;i++ )
{
if ((i % 2 == 0 || i % 3 == 0 || i % 5 == 0 || i % 7 == 0) && (i!=3 && i!=5 && i!=7) )
continue;
Console.WriteLine(i);
}

Well can you say this above mentioned snippet is normalized to the codes we done(i.e mentioned in this post) till now .. just a clarification ... can it be still optimized ??

Ty for your help
Vulpes my go to man any-time
Vulpes13y ago
There's nothing wrong with the logic, at least not in my adjusted version :)

If i is divisible by 2 then the for loop continues to the next value.

If i is divisible by 3, 5 or 7 (but not 3,5 or 7 themselves) then the for loop continues to the next value.

What's left must be prime and so is printed to the console.
SUNIL GUTTA13y ago
Hey vulpes ..

Well i tried using debugging i.e to check flow of code :)

actually problem is while executing when staring IF condition is satisfied i.e if(i%2) then it is going to continue then to for loop .. but the same flow is not same in case of second if statement i.e if(i%3) its not going on to continue when lets say i=9 . instead it going further for checking if conditions which are not necessary:)

Note: when i used curly braces for each continue .. debugging working fine .. ..

Why is issue ???
Vulpes13y ago
Incidentally, you could omit these lines altogether:

if (i % 11 == 0 && i != 11)
continue;

because the cases 22, 33 and 44 will be picked up as multiples of 2,3 and 2 respectively.