Question

I am writing a Little Man computer simulation and i want to overload the Indexing operator []. I have create a class called LMC and have done the following:

#include <iostream>

using namespace std;

class LMC
{
   public:
       LMC();
       void display();
       int& operator[](int index);
       ~LMC();
   private:
       int **array;
};

LMC::LMC()
{
   array = new int*[100];
   for(int i = 0; i < 100; i++)
   {
       array[i] = new int[3];
   }
   return array;
}

void LMC::display()
{
    for(int i = 0; i < 100;i++)
    {
       for(int j = 0; j <3;j++)
       {
          array[i][j] = 0;
          array[i][2] = i;
          cout << array[i][j]<<" ";
       }
       cout << endl;
    }
 }
 int& LMC::operator[](int index)
 {
    return array[index][2];
 }

  LMC::~LMC()
  {
     for(int i =0; i < 100 ; i++)
     { 
        delete [] array[i];
     }
     delete [] array;
     array = NULL;
  }

  int main()
  {
     LMC littleman;
     while(true)
     {
         int mailbox;
         int function;
         cout << "What is Mailbox number?" << endl;
         cin >> Mailbox;
         cout << "What is the function you want to use?" <<endl;
         cin >> finction;
         //the function is numbers eg 444 and 698;
         littleman.display();
         littleman[Mailbox] = function;
      }
     return 0;
}

I can run the program with no error. When i state that mailbox = 0 and function = 123 the is no problem.

This is displayed:

0 0 0
1 0 0
2 0 0
3 0 0
//continuing to 99

This display is wrong. The following must be displayed:

0 0 123
1 0 0
2 0 0
//continuing to 99

Do i have a logical error or am i overriding the array to display the original and how can i fix it?

Answer 1

These lines

  array[i][j] = 0;
  array[i][2] = i;

in LMC::display() destroy the contents of the array you’re trying to display.

Furthermore, there’s an extra semicolon at the end of void LMC::display();, so your code is not supposed to compile.