power function is giving wrong output in C++

Question

#include<iostream>
#include<cmath>
using namespace std;
int binary_conversion(int e,int w,int q,int n,int i)
{
  while(abs(w)>=1){//abs(e) to ensure that for negative numbers
    if(abs(w)>=1){
      e=w%2;
      w=w/2;
    }
    else
    {
      w=0;
    }cout<<"i is"<<i<<"\n";cout<<"q is before"<<q<<"\n";
       int r=pow(10,i);cout<<" r is"<<r;
    q=q+pow(10,i)*e;cout<<"q is"<<q<<"\n";
    i++;
 } return q ;
}
int main(){
  int n,w,q=0;int i=0,e;
  cin>>n;w=n;e=n;
  binary_conversion(e,w,q,n,i);
  cout<<q;
}

This program converts an integer to a binary digit. The error that I'm getting in this program is it's not giving 10^i value correctly. The line from where it's not giving the desired output is

q=q+pow(10,i)*e;cout<<"q is"<<q<<"\n";

the value of i in the 3rd iteration is 2 and 10^i should be 100, but it's 99. Any suggestion would be appreciated.

Answer 1

Your expression 10^i can be expressed iteratively:

int power_10 = 1;
int value = 0;
for (int j = 0; j < i; ++j)
{
  power = power * 10;
}

The above code does not involve floating point so there will be no loss from conversions.

You may want to change your expression evaluation to an iterative method.