Sum of cubes giving wrong answer?

[Arslan7041]

The following is the program im trying to write:

Write a program that asks the user to type an integer N and computes the sum of the cubes from 5^3 to N^3.

My only problem is that the answer printed to the screen is always 1 less than the correct answer, and I can't figure out why.

  #include <iostream>
#include <cmath>

using namespace std;

int main()
{
    int N, a, sum=0;

    cout << "Type in any integer greater than 5:" << endl << endl;
    cin >> N;
    while(cin.fail() || N<=5)
    {
        cout << "Invalid Entry. Try again:" << endl;
        cin.clear();
        cin.ignore();
        cin >> N;
    }

      for(int i=5; i<=N; i++)
      {
        a = pow(i, 3);
        sum+=a;
      }

    cout << "\n\nSum of the subes from 5 to " << N << " is: "
        << sum << "\n\n";

}

What am I doing wrong here?

[Drakonaut]

Based on cpp.sh, it is correct?

What do you mean "lesser by 1"? Like 5^3 to 6^3 is 340? I ran it and it computes 341.

[pnoid]

Your code worked for me. I used 6, 7, 8, 9, and 10 for N and it was right every time.

[Arslan7041]

Thats weird, it comes out as incorrect for me.

I just tried 6 and 7 and 10, and the output is always 1 less than the correct answer i.e. If I enter a 7, output is 683 when it should be 684.

Why are you guys getting the correct answer and im not?

[Arslan7041]

I just ran it in the cpp shell. Its works fine there.

However, if I run it in my codeblocks compiler, I always get an output 1 less than the correct answer.

Any idea why this is happening?

[pnoid]

I have no idea. I ran it visual studio and it worked fine.

[Arslan7041]

See "EXERCISE 6": http://en.wikibooks.org/wiki/C%2B%2B_Programming/Exercises/Iterations


I just tried the first solution and the output comes out fine. I enter a 6 and the output is 341.


But as soon as I run my own program, the output comes out wrong, always 1 less than the correct answer.

Is there something wrong with my code? But then how does it work for others?

Im really curious as to whats happening here. Any help would be appreciated.

[Momothegreat]

What editor and compiler are you using?

[Arslan7041]

CodeBlocks 12.11