#include <iostream>
#include <list>
#include <cmath>
 
using namespace std;
 
#define NUM_COLS 4
 
int sortByColumnN = 0;
 
class ItemRow{
public:      
   int columns[NUM_COLS];
 
   // this lets us sort the items
   bool operator<(ItemRow &rhs){
      return columns[sortByColumnN] < rhs.columns[sortByColumnN];
      }  
 
   void display(){
      for(int i = 0; i < NUM_COLS; i++){
         cout << columns[i] << ", ";
         }
      cout << endl;
      }
   };
 
main(){
   list<ItemRow> myList;
 
   for(int i = 0; i < 10; i++){
      ItemRow thisRow;
 
      for(int j = 0; j < NUM_COLS; j++){
         thisRow.columns[j] = rand() % 30;
         }
 
      myList.push_back(thisRow);
      }
 
   // display unsorted
   for(list<ItemRow>::iterator it = myList.begin(); it != myList.end(); it++){
      it->display();
      }
 
   myList.sort();
 
   cout << endl << endl << endl;
 
   // display sorted
   for(list<ItemRow>::iterator it = myList.begin(); it != myList.end(); it++){
      it->display();
      }
 
   // let's sort by the second column
   sortByColumnN = 1;
   myList.sort();
 
   cout << endl << endl << endl;
 
   // display sorted
   for(list<ItemRow>::iterator it = myList.begin(); it != myList.end(); it++){
      it->display();
      }
 
   system("pause");
   }