Conversion from double to integer

Question

I am stuck in problem where the double number is not getting properly converted to integer.

In this case->

int x=1000;

double cuberoot=pow(x,(1/(double)3));

int a=cuberoot;

cout<<"cuberoot="<<cuberoot<<endl;

cout<<"a="<<a<<endl;

Output:

cuberoot=10
a=9

Why here a=9 and not 10?

Any solution to this problem??

Also I don't want to round the value..if a=3.67 then it should be converted to 3 only and not 4.

You can add a small positive to number and then calculate the root. Like `x=1000+0.05`. This would give `a=10`. — , Jun 14 '14 at 18:03

yizzlez · Answer 1 · 2014-06-14T18:11:12.007

1

Because the cuberoot is very close to 10 but not quite 10. std::cout truncates and rounds the number to 10, but a double to integer conversion will strip the decimal which is why a = 9. To solve this problem, you can use std::round():

int a=round(cuberoot);

edited Jun 14 '14 at 18:11

answered Jun 14 '14 at 17:59

yizzlez

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So any solution to this so that a=10 here? – user2826957 Jun 14 '14 at 18:01
use a round() function. – OldProgrammer Jun 14 '14 at 18:01
Actually problem is I don't want to round exactly. – user2826957 Jun 14 '14 at 18:04
I want that if a=3.99 then it should be converted to 3 only....any solution to this? – user2826957 Jun 14 '14 at 18:05
Right now `cube = 9.99...` and it is converting that to `a=9` – yizzlez Jun 14 '14 at 18:06
In above case where cuberoot=10 and when converted to int is 9 which i don't want...it should remain 10 as it is! – user2826957 Jun 14 '14 at 18:07
`cuberoot != 10`, it is equal to `9.9999999999999982...`. `cout` rounds when displaying the number – yizzlez Jun 14 '14 at 18:09

score 0 · Answer 2 · answered Jun 14 '14 at 18:03

Try this and see why!

#include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

int main(){
    int x = 1000;
    double cube = pow(x, 1.0/3.0);
    int a = cube;
    cout<<"cube="<< fixed << setprecision(16) << cube<<endl;
    cout<<"a="<<a<<endl;
}

Conversion from double to integer

2 Answers2

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