<aside> 💡 Key Concept

This week you will learn about object interactions, modelling real world items with classes and static and non-static functions.

Learning Objectives

• Use object interactions to achieve complex functionality through a simple command sequence
• Explain how to model a familiar real world entity as a class with data and functions
• Decide when it is appropriate to use static or non-static functions </aside>

Starter code

5.1. The wallet class

First, let’s implement the wallet class’s header file Wallet.h. The wallet class contains the following functions:

• Wallet(): the class constructor that takes 0 argument
• insertCurrency: insert currency and amount into the wallet
• removeCurrency: remove an indicated currency with the indicated amount.
• toStrong: get the currencies and the respective amounts in the wallet

#include <string>
#include <map>

class Wallet
{
public:
    Wallet();
    /** insert currency to the wallet */
    void insertCurrency(std::string type, double amount);
    /** remove currency to the wallet */
    bool removeCurrency(std::string type, double amount);
    /** check if the wallet contains this much currency or more */
    bool containsCurrency(std::string type, double amount);
    /** get the currencies and the respective amounts in the wallet */
    std::string toString();

private:
    std::map<std::string, double> currencies;
};

Next, let’s create the wallet cpp file Wallet.cpp and its skeleton, i.e., minimal code that allows the file to compile. What I normally do is to copy the function declaration from the header file to the cpp file, then add class scope to each function (e.g. Wallet:: ) and change the ; to {} . If the function declare a return type, return a minimal value with that type.

#include "Wallet.h" 

Wallet::Wallet() {
    
}
/** insert currency to the wallet */
void Wallet::insertCurrency(std::string type, double amount)
{

}

/** remove currency to the wallet */
bool Wallet::removeCurrency(std::string type, double amount) {
    return true;
}

/** check if the wallet contains this much currency or more */
bool Wallet::containsCurrency(std::string type, double amount)
{
    return false;
}

std::string Wallet::toString()
{
    return "s";
}

In MerkelMain.h file, include the Wallet.h and introduce a private Wallet object.

//...
#include "Wallet.h"

class MerkelMain
{
    private: 
        // ...
        Wallet wallet;
};

Go to MerkelMain.cpp, in the init function, call the insertCurrency function to insert some dummy currency.