Whats causes bug in my c++ code?

Question

I tried writing a code, which is supposed to calculate 4 - 4/3 + 4/5 - 4/7 + 4/9 +... but it keeps printing "3" as the answer.

#include <iostream>
#include <math.h>
#include <conio.h>

using namespace std;

int main()
{
    int s=0,a,n;
    cin>>n;
    for(int i=0 ; i<=n ; i++)
    {
        a=(4/((2*i)+1))*pow(-1,i);
        s=s+a;
    }
    cout<<s;
    return 0;
}

each number has an id from 0 to infinity . as an example if you set 2 as an "n" 's value , it will count 4 - 4/3 — Sina, Nov 01 '15 at 19:15
haha yeah i know right . i dont even know why did i add that include — Sina, Nov 01 '15 at 19:17
It would help if you'd bother to use capital letters and punctuation. _"dude im just a starter lol"_ this is not a school chatroom. — Lightness Races in Orbit, Nov 01 '15 at 19:19

score 5 · Accepted Answer · edited May 23 '17 at 11:44

5

You are using integer division, so your series converges really, really quickly.

Make s and a be doubles, and replace 4 with 4.0.

edited May 23 '17 at 11:44

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answered Nov 01 '15 at 19:17

Lightness Races in Orbit

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Thanks so much dude . – Sina Nov 01 '15 at 19:21
5

@Sina: I'm not your "dude". Regardless, you are welcome. – Lightness Races in Orbit Nov 01 '15 at 19:22
I think you'll have to transform your (2*i) into (2.0*i) too or you'll still have an integer division. – Chris R. Nov 01 '15 at 19:23
@ChrisR.: You are mistaken. – Lightness Races in Orbit Nov 01 '15 at 19:23

Whats causes bug in my c++ code?

1 Answers1