为什么这样在屏幕上不打印任何内容？

Question

#include <iostream>

using namespace std;

class A
{
    public:
    int index;
    int t;
    int d;
    int sum;
};

A arr[1000];

bool comp (const A &a, const A &b)
{
    if (a.sum < b.sum)
        return true;
    else if (a.sum == b.sum && a.index < b.index)
        return true;
    return false;
}
int main (void)
{
    int n,foo,bar,i;
    i = 0;
    cin>>n;
    while ( n != 0 )
    {
        cin>>foo>>bar;
        arr[i].index = i+1;
        arr[i].t = foo;
        arr[i].d = bar;
        arr[i].sum = arr[i].t+arr[i].d;
        n--;
        i++;
    }
    sort(arr,arr+n,comp);
    for ( int j = 0; j < n; j++ )
        cout<<arr[j].index;
    cout<<"\n";
    return 0;
}

So, I made this program which accepts values from users, and then sorts them on the basis of a specific condition. However, when I try to print the values of the array, it doesn't print it. I don't know why. Please help. Thanks!

PS: I even tried to print the value of the array without use of comparator function, but still it doesn't print.

Edit: Got my error, as mentioned by some amazing people in the comments. However, on inputting the values as,

5
8 1
4 2
5 6
3 1
4 3

It should return the answer as 4 2 5 1 3 but instead it returns 1 2 3 4 5 . Basically, it sorts according to the sum of the 2 elements in each row and prints the index. What might be the problem?

Answer 1

It is not sorting because you are modifying the value of n in the while loop.

So, when n = 0 after the loop ends, there is nothing to sort (or to print later for that matter):

sort( arr, arr + n, comp);

is equivalent to

sort( arr, arr + 0, comp);

Easiest approach would be to use a for loop:

for( int i=0; i<n; ++i )
{
    ....
}

This way, n remains unchanged.