Category: C++

#include < iostream >
using namespace std;

int main()
{
    int *p;
    
    p = new int;
    if(!p) {
        cout << "memory set error\n";
        return 1;
    }
    
    *p = 1000;
    cout << "p point integer is: " << *p << "\n";
    delete p;
    return 0;
}

#include < iostream >
using namespace std;

class samp {
    int a, b;
public:
    samp(int n, int m){ a = n; b = m; }
    int get_a() { return a; }
    int get_b() { return b; }
};

int main()
{
    samp ob[4][2] = {
        samp(1, 2), samp(3, 4),
        samp(5, 6), samp(7, 8),
        samp(9, 10), samp(11, 12),
        samp(13, 14), samp(15, 16)
    };
    
    int i;
    
    for(i = 0; i<4; i++){
        cout << ob[i][0].get_a() << ' ';
        cout << ob[i][0].get_b() << "\n";
        cout << ob[i][1].get_a() << ' ';
        cout << ob[i][1].get_b() << "\n";
        
    }
    cout << "\n";
    return 0;
}

#include < iostream >
using namespace std;

class samp {
    int a;
public:
    samp(int n){ a = n; }
    int get_a() { return a; }
};

int main()
{
    samp ob[4][2] = {
        1, 2,
        3, 4,
        5, 6,
        7, 8
    };
    int i;
    
    for (i=0; i<4; i++){
        cout << ob[i][0].get_a() << ' ';
        cout << ob[i][1].get_a() << "\n";
    }
    cout << "\n";
    
    return 0;
}

#include 
using namespace std;

class samp {
    int a;
public:
    samp(int n){ a = n; }
    int get_a() { return a; }
};

int main()
{
    samp ob[4] = { -1, -2, -3, -4 };
    int i;
    
    for(i=0; i<4; i++) cout << ob[i].get_a() << ' ';
    cout << "\n";
    
    return 0;
}

オブジェクトは変数であり、他の型の変数と同じ機能と属性を持っています。

#include < iostream >
using namespace std;

class samp {
    int a;
public:
    void set_a(int n) { a = n; }
    int get_a() { return a; }
};

int main()
{
    samp ob[4];
    int i;
    
    for(i=0; i<4; i++) ob[i].set_a(i);
    for(i=0; i<4; i++) cout << ob[i].get_a();
    
    cout << "\n";
    
    return 0;
}

二つの異なる型のクラスが共通の特性を持っているとき、それを比較する。

#include < iostream >
using namespace std;

class truck;

class car {
    int passengers;
    int speed;
public:
    car(int p, int s){ passengers = p; speed = s; }
    friend int sp_greater(car c, truck t);
};

class truck {
    int weight;
    int speed;
public:
    truck(int w, int s){ weight = w, speed = s; }
    friend int sp_greater(car c, truck t);
};

int sp_greater(car c, truck t)
{
    return c.speed - t.speed;
}

int main()
{
    int t;
    car c1(6, 55), c2(2, 120);
    truck t1(10000, 55), t2(20000, 72);
    
    cout << "c1 and t1 compare:\n";
    t = sp_greater(c1, t1);
    if(t<0) cout << "truck is faster\n";
    else if(t==0) cout << "car and truck speed is same\n";
    else cout << "car is faster\n";
    
    cout << "\nc2 and t2 compare:\n";
    t = sp_greater(c2, t2);
    if(t<0) cout << "truck is faster\n";
    else if(t==0) cout << "car and truck speed is same\n";
    else cout << "car is faster\n";
    
    return 0;
}

関数からそのクラスの非公開メンバにアクセスしたいとき。

#include < iostream >
using namespace std;

class myclass {
    int n, d;
public:
    myclass(int i, int j){ n = i; d = j; }
    friend int isfactor(myclass ob);
};

int isfactor(myclass ob)
{
    if(!(ob.n % ob.d)) return 1;
    else return 0;
}

int main()
{
    myclass ob1(10, 2), ob2(13, 3);
    
    if(isfactor(ob1)) cout << "2 is 10 factor\n";
    else cout << "2 is not 10 factor \n";
    
    if(isfactor(ob2)) cout << "3 is 13 factor \n";
    else cout << "3 is not 13 factor \n";
    
    return 0;
}

#include < iostream >
#include < cstring >
using namespace std;

class samp{
    char s[80];
public:
    void show() { cout << s << "\n"; }
    void set(char *str) { strcpy(s, str); }
};

samp input()
{
    char s[80];
    samp str;
    
    cout << "type character: ";
    cin >> s;
    
    str.set(s);
    
    return str;
}

int main()
{
    samp ob;
    
    ob = input();
    ob.show();
    
    return 0;
}

オブジェクトのコピーを作成すると、コンストラクタ関数は呼び出されません。

#include < iostream >
using namespace std;

class samp {
    int i;
public:
    samp(int n ){
        i = n;
        cout << "call contractor \n";
    }
    ~samp() { cout << "call destroctor\n"; }
    int get_i() { return i; }
};

int sqr_it(samp o)
{
    return o.get_i() * o.get_i();
}

int main()
{
    samp a(10);
    cout << sqr_it(a) << "\n";
    
    return 0;
}

オブジェクトがpass by valueによって関数に渡されます。

#include < iostream >
using namespace std;

class samp{
    int i;
public:
    samp(int n){ i = n; }
    int get_i() { return i; }
};

int sqr_it(samp o)
{
    return o.get_i() * o.get_i();
}

int main()
{
    samp a(10), b(2);
    cout << sqr_it(a) << "\n";
    cout << sqr_it(b) << "\n";
    
    return 0;
}