Re: Virtual functions

"osmium" <>
Sat, 17 Mar 2007 12:34:48 -0800
"Wilson" writes:

hi, i am trying to understand virtual functions, both how to create
them and how or when to use them - how they can be used to improve a
program. Below is a very simple program which i quickly made using
information gathered from a book on the subject, however this simply
returns a blank space. please help both on this program and anything
else related to virtual functions.


#include <cstdio>
#include <cstdlib>
#include <iostream>
using namespace std;

class account
            int balance, number;
            int function() { cout << balance; }
class checking : public account
            int balancechecking;

You are off to a bad start. The balance should be a member of the base

Take a look at this. I am sure you can see how things such as service
charge and interest rate could be made a part of the class, for simplicity I
coded these constants in the functions. The order of doing things in main
was dictated by the order of testing,, which is not representative of an end
user application.

#include <iostream>

using namespace std;

class Acct
     virtual void add_int() = 0;
     void show() { cout << balance << endl;}
     double balance;
class Checking : public Acct
     Checking(double bal) {balance = bal;}
     void add_int() {balance -= 15;} // monthy "service" fee
class Savings : public Acct
     Savings(double bal) {balance = bal;}
     void add_int() {balance *= 1.01;}
int main()
   Acct* arr[2];
   arr[0] = &Checking(256);
   arr[0] -> add_int();
   arr[0] -> show();

   arr[1] = &Savings(1024);
   arr[1] -> add_int();
   arr[1] -> show();


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