double value to int variable- unexpected output

Question

Here is a simple piece of code. actually it is a "fill array" function code.

#include <iostream>
 using namespace std;
int main(){ 
   int size = 10; a[10]; numberUsed;
   cout << "Enter up to " << size << " nonnegative whole numbers.\n"
   << "Mark the end of the list with a negative number.\n";
   int next, index = 0;
   cin >> next;
   while ((next >= 0) && (index < size)){
      a[index] = next;
      index++;
      cin >> next;
   }
  numberUsed = index;
  for(int i = 0 ; i < numberUsed -1 ; i++){
 cout << a[i]  << endl;
  }
}

it works fine when user enters integers. But when i enter double values it should trancate that particular value. and repeats that value for the next entered integers also. so now for input 1 2 3 4 5 6.5 7 8 9 -1 .I get the following output 1 2 3 4 5 6 6 6 6 6 Any help will be appreciated.

Answer 1

You told cin to read an integer, so that's what it's going to do - it will stop as soon as it sees a character that isn't valid for an integer. In this case it's the '.'. Trying to read more integers will just continue to fail, in your case leaving next at its previous value.

If you want to truncate a floating point value, read into a floating point variable and then do the truncation yourself.

double next;
...
a[index] = (int) next;

Answer 2

When reading integer values (and your code is using int next;, anything that isn't an integer will "stop" the input from every reading anything else. Since next is 6 at the point when it hits a '.' in the input stream, it continues to fill the array with that value until it runs out of space.

If you check the status of the input, e.g. if(!cin >> next) ... error handling ...;, you can detect when things have gone wrong. As part of the error handling, you should then "ignore any input until a whitespace" - cin.ignore(1000, ' '); would be a good start. You will also need to reset the error flag on cin to not get an error next time, with cin.clear() will do that.

If you want to input floating point numbers, you need to use float or double type for next (and the array a).