If you are debugging code (and that is what you are doing here), you need to step through the code and check your assumptions. That can be done with a traditional debugger that lets you see each line as it is run, or by putting some output statements in the code.

Your errors include
(a) the loop for the factorial never is run. since neither N nor i are changed in the while loop. This should be fairly obvious since you never reached the "factoraila == " statement

(b) you are using a loop to calculate [tex]\sum n^2[\tex] ?? There are simple formula to get the result, no loop.

C++ Syntax (Toggle Plain Text)

while (N>1 && i>=0)
 
 { fact = fact * (N-i);
     i = i+1;
   }

while (N>1 && i>=0) { fact = fact * (N-i); i = i+1; }

Yes, i changes, but not in a way that will get you out of this loop. N doesn't change, so this is an infinite loop. Once inside, you'll never get out (well, eventually, after i overflows, you might possibly get out, but that'll take a few billion iterations). Change the conditions on your while loop so that it is no longer an infinite loop.

aha ... so the problem is with the condition .. exactly in using (&&) ?