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Help: Code Sum/Factorial

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Help: Code Sum/Factorial

 
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  #1
Oct 21st, 2009
Dear all,

There is some errors in the code that I can’t seem to spot.

The code is

C++ Syntax (Toggle Plain Text) 
  1. # include <iostream> 
  2. using namespace std;
  3. int main () 
  4. {
  5.  
  6. int N;       // Declaring and initializing variables
  7. int n=0; 
  8. int i=0; 
  9. int fact=1; 
  10.  
  11. cout << "Please Enter an Integer" << endl; // The prompt
  12. cin >> N; // To read from the keyboard
  13.  
  14. // Part a
  15.  
  16. if (N==1 || N==0) 
  17. { cout << "The Factorial of " << N << " = 1" << endl; } // Because it's known that the fact. of 0/1 = 1
  18.  
  19.  
  20. while (N>1 && i>=0)
  21.  
  22.  { fact = fact * (N-i);
  23.      i = i+1;
  24.    }
  25.  
  26.  
  27. cout << "The factorial of " << N << " = " << fact << endl;
  28.  
  29. // Part b
  30.  
  31. for ( int sigma=0; n=0 || n<=N ; n++)
  32. { sigma = sigma + (n*n);
  33. }
  34.  
  35.  
  36. return 0;
  37.  
  38.  
  39. }

and the question is attached
Last edited by new programer; Oct 21st, 2009 at 6:05 am.
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  #2
Oct 21st, 2009
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.
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  #3
Oct 21st, 2009
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Originally Posted by StuXYZ View Post
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.
How come it is not changing in part (a) I did increament it

(b) I am using the baisc concept of it "Mathematically ... should it be altered somehow ?
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  #4
Oct 21st, 2009
//Any help, remarks would be appreciated
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  #5
Oct 21st, 2009
C++ Syntax (Toggle Plain Text) 
  1. while (N>1 && i>=0)
  2.  
  3.  { fact = fact * (N-i);
  4.      i = i+1;
  5.    }

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.
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  #6
Oct 21st, 2009
For me, in these situations, its always easier to set up a for loop.

For instance you could have...
C++ Syntax (Toggle Plain Text) 
  1. for(int i = 1; i <= n; i++)
  2. {
  3. // Factorial code goes here
  4. }

This way the code in the for loop keeps repeating until i is greater than n, which solves your problem of an infinite loop.
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  #7
Oct 21st, 2009
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Originally Posted by VernonDozier View Post
C++ Syntax (Toggle Plain Text) 
  1. while (N>1 && i>=0)
  2.  
  3.  { fact = fact * (N-i);
  4.      i = i+1;
  5.    }

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 (&&) ?
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  #8
Oct 21st, 2009
And how come part b is not working ??
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  #9
Oct 21st, 2009
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Originally Posted by new programer View Post
aha ... so the problem is with the condition .. exactly in using (&&) ?
No its not just the &&, its the whole statement. You need to rethink your condition. The one you have now is incorrect. Take a look at my earlier post for ideas.
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  #10
Oct 21st, 2009
I did correct it. That was for part a

and I modified part b .. as follows
C++ Syntax (Toggle Plain Text) 
  1. // Part b
  2. cout << "Please Enter an Integer" << endl; // The prompt
  3. cin >> N; // To read from the keyboard
  4.  
  5.  
  6. sum=0;
  7. for ( n=0 ; n<=N ; n++)
  8. { 
  9. 	sum = sum + (n*n);
  10. }
  11.  
  12. return 0;
  13.  
  14.  
  15. }

It did not use to appear so I thought I would add the prompt again

the prompt appeared and I entered the number but then it terminates

I think I don't have to put the prompt again .. maybe there's something wrong with the code at part b .. any hints?
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