程序设计实习作业 02 各种构造函数和析构函数

//输出 9 22 5


#include <iostream>
using namespace std;
class Sample {
public:
    int v;
    Sample(int n){
        v = n ;
    }
    Sample(){
        
    }
    Sample(const Sample & a){
        v = a.v + 2;
    }
    
};
void PrintAndDouble(Sample o)
{
    cout << o.v;
    cout << endl;
}
int main()
{
    Sample a(5);
    Sample b = a;
    PrintAndDouble(b);    //注意这里调用了复制构造函数
    Sample c = 20;
    PrintAndDouble(c);    //注意这里调用了复制构造函数
    Sample d;
    d = a;
    cout << d.v;     //本来是5，用printanddouble输出就多了2
    return 0;
}

//先输出123
然后输出 m，n


#include <iostream>
using namespace std;
class A {
    public:
        int val;

        A(int a){
            val = a;
        }
        
        A(){
            val = 123;
        }        
        A & GetObj(){
            return *this;   //返回 GetObj成员函数 作用的对象
        }
    
};
int main()
{
    int m,n;
    A a;
    cout << a.val << endl;
    while(cin >> m >> n) {
        a.GetObj() = m;
        cout << a.val << endl;
        a.GetObj() = A(n);
        cout << a.val<< endl;
    }
    return 0;
}

//重载 ”=“ 给复数赋值

#include <iostream>
#include <cstring>
#include <cstdlib>
using namespace std;
class Complex {
private:
    double r,i;
public:
    void Print() {
        cout << r << "+" << i << "i" << endl;
    }
    
    Complex operator=(const char* a){
        string s = a;
        int pos = s.find("+",0);   //从0号开始查找“+“的位置
        string sTmp = s.substr(0,pos);   // 不考虑“”  从第0位开始截取长度为pos的字符串 此处pos=1
        r = atof(sTmp.c_str());
        string sTmp1 = s.substr(pos+1,s.length()-2-pos);  // 从pos+1位开始截取s.length-2-pos长度的字符串 此处为1

//封闭类对象的初始化

    
#include <iostream>
#include <string>
using namespace std;
class Base {
public:
    int k;
    Base(int n):k(n) { }
};
class Big
{
public:
    int v;
    Base b;
    
    Big(int n):v(n),b(n){    //直接调用成员对象的类型转换构造函数
    }
    
};
int main()
{
    int n;
    while(cin >>n) {
        Big a1(n);
        Big a2 = a1;
        cout << a1.v << "," << a1.b.k << endl;
        cout << a2.v << "," << a2.b.k << endl;
    }
}

//复制构造函数 和 析构函数 在临时对象生成时的作用

#include <iostream>
using namespace std;
class Apple {
    public:
    static int nTotalNumber;   //全局变量
    Apple(){
        nTotalNumber ++;    //无参初始化的时候 总数加一
    }
    ~Apple(){
        nTotalNumber --;   //临时变量消失时 总数也减一
    }
    static void PrintTotal() {
        cout << nTotalNumber << endl; 
    }

};
int Apple::nTotalNumber = 0;
Apple Fun(const Apple & a) {
    a.PrintTotal();
    return a;
}
int main()
{
    Apple * p = new Apple[4];    //无参构造函数调用4次
    Fun(p[2]);    //Fun函数的返回值是Apple类型的临时对象，消失时使得总数减一
    Apple p1,p2;  //无参构造函数调用两次
    Apple::PrintTotal ();   //4-1+2
    delete [] p;  //5-4
    p1.PrintTotal ();
    return 0;
}

        i = atof (sTmp1.c_str());
        return *this;
    }
    
    
};
int main() {
    Complex a;
    a = "3+4i"; a.Print();
    a = "5+6i"; a.Print();
    return 0;
}