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Classes with methods in C++

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• Class methods
  • Class methods in C++ resembles that of Java, except for the fact that C++ makes a distinction between:

    Method definition: The definition of a method consists of the method signature (= name of method + number and type of parameters) AND the method body (= program statements) Method declaration: The declaration of a method consists only of the method signature (= name of method + number and type of parameters)

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  • Java requires that the class methods be defined inside the class definition

    Example:

    public class BankAccount { private double balance; // Constructors public BankAccount() { balance = 0; } public BankAccount(double x) { balance = x; } // Ordinary methods public void deposit(double amount) { balance = balance + amount; } public void withdraw(double amount) { balance = balance - amount; } public double getBalance() { return(balance); } }

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  • How to use the class:

    import BankAccount; // <--- Must be done. // Java made it easy: put class in same directory // and Java will look for the class to import public class myProgram { main().... }

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  • In C++, you have the option to:

    Define the method inside the class Such functions/methods are called in-line functions (C++ programmers usually write short functions in-line) Define the method outside the class in a separate file

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• In-line functions
  • The BankAccount class (that's true for any class) written using in-line in C++ resembles Java

    Example:

    class BankAccount { private: double balance; public: // Constructors BankAccount() { balance = 0; } BankAccount(double x) { balance = x; } // Ordinary methods void deposit(double amount) { balance = balance + amount; } void withdraw(double amount) { balance = balance - amount; } double getBalance() { return(balance); } };

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  • How to use the class:

    #include "BankAccount.C" // Need to include class declaration/definition int main(int argc, char *argv[]) { BankAccount x, y(1000); cout << "x = " << x.getBalance() << endl; cout << "y = " << y.getBalance() << endl; x.deposit(100); y.withdraw(100); cout << "x = " << x.getBalance() << endl; cout << "y = " << y.getBalance() << endl; }

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  • Example Program: (Demo above code)                                                
    • The BankAccount class Prog file: click here
    • The test program file: click here

    How to run:

    CC TestBankAccount.C a.out

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• Separating declaration and definition
  • It is common in C++ to separate the function definitions and the function declarations - especially when the function definition is lengthy

    The declaration part and the definition part are usually stored in separate files

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  • The declaration part of the BankAccount class is as follows:

    class BankAccount { private: double balance; public: // Constructors BankAccount(); BankAccount(double x); // Ordinary methods void deposit(double amount); void withdraw(double amount); double getBalance(); };

    This is stored in BankAccount.h (this is usually called a header file)

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  • The definition part of the BankAccount class is as follows:

    include "BankAccount.h" // Include declaration first ! // Constructors BankAccount::BankAccount() { balance = 0; } BankAccount::BankAccount(double x) { balance = x; } // Ordinary methods void BankAccount::deposit(double amount) { balance = balance + amount; } void BankAccount::withdraw(double amount) { balance = balance - amount; } double BankAccount::getBalance() { return(balance); } };

    (The BankAccount:: notation tells C++ that the function/method is a member method in the class BankAccount)

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  • How to use the class:

    #include "BankAccount.h" // Need to include class declaration/definition ^^^^ (declaration file) int main(int argc, char *argv[]) { BankAccount x, y(1000); cout << "x = " << x.getBalance() << endl; cout << "y = " << y.getBalance() << endl; x.deposit(100); y.withdraw(100); cout << "x = " << x.getBalance() << endl; cout << "y = " << y.getBalance() << endl; }

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  • Example Program: (Demo above code)                                                
    • The BankAccount declaration file: click here
    • The BankAccount implementation Prog file: click here
    • The test program file: click here

    How to run:

    CC -c BankAccount.C CC -c TestBankAccount.C CC TestBankAccount.o BankAccount.o or: CC BankAccount.C TestBankAccount.C Run: a.out