While loop 2

[malola123]

Hi,

Im normally pretty good with loops, but for some reason, im not able to understand this loop.

using System;

class Ques
{
public static void Main()
{
int i = 17;
while(i != 1)
{
Console.WriteLine("{0}", i);
i = 3*i + 1;
while(i%2 == 0)
i/=2;
}
}
}

The answer for this loop is: 17, 13, 5.

Can someone explain the process in each iteration? Thanks!

 

[TipGiver]

Yep..

At the begginning, i=17.

The while(i != 1) will loop as long as i is not equal to 1.

Print the 'i' (17).

Do calculations.. i = 3*17 + 1 = 51+1 = 52

The following:
while(i%2 == 0)
i/=2;

will loop (and do the i = i/2) as long as the module of i by 2 is equal to 0. So, in other words, it will loop as long as the 'i' is even number!

So...
'i' becomes 52/2 = 26 (even)
'i' becomes 26/2 = 13 (odd.. so stop) and go to the outer loop because 13 is not equal to 1.

Print the 'i' (13).

i = 3*13 + 1 = 39 + 1 = 40 (even ! so go in the other loop)

'i' becomes 40/2 = 20 (even)
'i' becomes 20/2 = 10 (even)
'i' becomes 10/2 = 5 (odd, stop now and go to the outer loop) because 13 is not equal to 1.

i = 3*5 + 1 = 15+1 = 16

'i' becomes 16/2 = 8 (even)
'i' becomes 8/2 = 4 (even)
'i' becomes 4/2 = 2 (even)
'i' becomes 2/2 = 1 (odd, stop now and do NOT go to the outer loop) because 13 is equal to 1).

So nothing is printed now, because the Console.WriteLine("{0}", i); is in the loop that we did not entered.


Phewww!

 

[malola123]

Wow, that was a great explanation!!..Thanks!!!

 

[TipGiver]

Thanks.

Forgot something...

Above:
i = 3*5 + 1 = 15+1 = 16
Put:
Print the 'i' (5).

 

[Zathras]

Google: "Collatz conjecture"

 

[chiph]

Is this for homework?

Chip H.


____________________________________________________________________
If you want to get the best response to a question, please read FAQ222-2244 first

 

[malola123]

lol...no no..im just trying to learn c# for myself...im a newbie to programming!