数组显示比正常结果更多的结果

Question

this is my code:

#include <iostream>
using namespace std;

int main()
{
  char character;
  int x;
  cout << "Input a character: " ;
  cin >> character;
  x = int(character);
  cout << "Its integer value is: " << x << endl;
  int arr[7], i=0,j;
  while(x>0)
  {
    arr[i]=x%2;
    i++;
    x=x/2;
  }
  cout << "Its Binary format is: ";
  for (j=i; j>=0;j--)
  {
    cout<<arr[j];
  }
  return 0;
}

I have only 8 array spaces allocated for this code but the displayed result is more than 8 and is totally unrelated to the algorithm. I'm suspecting this to be an overflow issue. How do i remedy this issue? Thank you!

Answer 1

while(x>0)
{
    arr[i]=x%2;
    i++;
    x=x/2;
}

let's take case when this loop is executed once. i is 1 after loop is finished. However, array element at index 1 is not initialized.

You trigger undefined behaviour by trying to print it here:

for (j=i; j>=0;j--) // assuming for should be here
{
    cout<<arr[j]; // access array element with index 1 (our example)
}

The fix is to change your loop to

for (j=i-1; j>=0;j--)

Also beware what if user enters number which is larger (or equal) than 7th power of 2. You won't have places in your array to store all digits. And will trigger again undefined behaviour, by trying to write past the end of the array.