類的建構函式專門用於構造新物件、將值賦給他們的資料成員。

// 類定義
// stock00.h

#ifndef STOCH00_H_
#define STOCH00_H_

#include<string>
using namespace std;

class Stock {
    private:
        std::string company;
        long shares;
        double share_val;
        double total_val;

        void set_tot() { total_val = shares * share_val; } //
 
 行內函數
    public:
        Stock(const string & co, long n = 0, double pr = 0.0); // 建構函式

        void acquire(const std::string & co, long n, double pr);
        void buy(long num, double price);
        void sell(long num, double price);
        void update(double price);
        void show();
};


 
#endif

// 成員函式實現
// stock00.cpp

#include<iostream>

#include "stock00.h"


void Stock::acquire(const std::string & co, long n, double pr) {
    company = co;
    if (n < 0) {
        std::cout << "Number of shares can't be negative;"
            << company << "shares set to 0.\n
 
";
    }
    else {
        shares = n;
    }
    share_val = pr;
    set_tot();
}
void Stock::buy(long num, double price) {
    if (num < 0) {
        std::cout << "Number of shares purchased can't be negative."
            << "Transaction is aborted.\n";
    }
    else {
        shares += num;
        share_val = price;
        set_tot();
    }
}
void Stock::sell(long num, double price) {
    using std::cout;
    if (num < 0) {
        cout << "Number of shares sold can't be negative."
            << "Transaction is aborted.\n";

    }
    else if(num > shares){
        cout << "You can't sell more than you have!"
            << "Transaction is aborted.\n";
    }
    else {
        shares -= num;
        share_val = price;
        set_tot();
    }
}
void Stock::update(double price) {
    share_val = price;
    set_tot();
}
void Stock::show() {
    std::cout << " Company: " << company<<'\n'
        << " Shares: $" << shares << '\n'
        << " Share Price: $" << share_val<<'\n'
        << " Total Worth: $" << total_val << '\n';
}

// 建構函式
Stock::Stock(const string & co, long n, double pr) {
    company = co;
    if (n < 0) {
        std::cerr << "Number of shares can't be negative; "
            << company << " shares set to 0.\n";
        shares = 0;
    }
    else {
        shares = n;
    }
    share_val = pr;
    set_tot();
}

// 類的使用
// usestock0.cpp

#include<iostream>

#include "stock00.h"

int main() {
    Stock fluffy_the_cat("NanoSmart", 20, 12.50); 
    fluffy_the_cat.show();

    return 0;
}