Why this code doesn't allow me to receive the whole array? - c++

Question

#include <bits/stdc++.h>
using namespace std;
string bin(int n){
string x="";
while(n!=0)
{
int z=n%2;
x+=to_string(z);
n%=2;
}
return x;
}
int main(){
int t;
cin>>t;
while(t--)
{
int n;
cin>>n;
int a[n];
for(int i=0;i<n;i++)
{
cin>>a[i];
string x=bin(a[i]);
int u=x.size();
int cnt=0;
for(int g=0;g<u;g++)
{
if(x[g]=='1')
++cnt;
}
cout<<cnt<<' ';
}
cout<<'\n';
}
}
This code is given several test cases and each test case will have an array of n integers, for each element in the array I should count the number of ones in the binary representation of it. I wrote a function that expects an integer and returns a string containing the binary representation of it. But I wonder why my code does not end, and not allowing me to receive other numbers in array.
For instance, there's one test case and and only array of 2 integers if I inputted 1 and wait for ever to enter the second number, what's happening?

Answer 1

This is your bin function reduced to the bare minimum:
string bin(int n){
while(n!=0)
{
n%=2;
}
return {};
}
If n is even you will set it to 0 on the first iteration, otherwise you set it to 1 and never change it afterwards (1%2==1). Hence you have a endless loop. I won't spoil you the "fun" of completing the exercise, so I will just point you to using a debugger. If you step trough your code line by line you could have observed how n never changes and why the loop wont stop.
PS: (spoiler-alert) you might want to take a look at std::bitset (end of spoiler)