c++ - Why doesn't this print anything on the screen? -

#include <iostream>  using namespace std;  class {     public:     int index;     int t;     int d;     int sum; };  arr[1000];  bool comp (const &a, const &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;     = 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);     ( int j = 0; j < n; j++ )         cout<<arr[j].index;     cout<<"\n";     return 0; } 

so, made program accepts values users, , sorts them on basis of specific condition. however, when try print values of array, doesn't print it. don't know why. please help. thanks!

ps: tried print value of array without use of comparator function, still doesn't print.

edit: got error, mentioned amazing people in comments. however, on inputting values as,

5 8 1 4 2 5 6 3 1 4 3 

it should return answer 4 2 5 1 3 instead returns 1 2 3 4 5. basically, sorts according sum of 2 elements in each row , prints index. might problem?

it not sorting because modifying value of n in while loop.

so, when n = 0 after loop ends, there nothing sort (or print later matter):

sort( arr, arr + n, comp); 

is equivalent

sort( arr, arr + 0, comp); 

easiest approach use for loop:

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

this way, n remains unchanged.