题1：实现下列程序，编译并运行，如果有错误请纠正(实验报告中写明出错的原因及相关知 识点)，并给出输出结果。 #include<iostream> usingnamespacestd; classBase{ public: Base(){a=5;cout<<"Basea="<<a<<endl;} protected: inta; }; classBase1:publicBase{ public: intb1; Base1(){a=a+10;cout<<"Base1a="<<a<<endl;} }; classBase2:publicBase{ public: intb2; Base2(){a=a+20;cout<<"Base2a="<<a<<endl;} }; classDerived:publicBase1,publicBase2{ public: intd; Derived(){ cout<<"Base1::a="<<Base1::a<<endl; cout<<"Base2::a="<<Base2::a<<endl; cout<<"Deriveda="<<a<<endl; } }; main(){ Derivedobj; return0; }

题1答案：

程序中存在以下几个错误：

1. 在类Base的构造函数中，缺少访问修饰符public，应该将Base()修改为public: Base()。

2. 在main函数中，缺少int类型的返回值，应该将main()修改为int main()。

3. 在Derived类的构造函数中，应该在Base1和Base2的构造函数中分别调用它们的构造函数，以初始化变量a，否则会出现未定义的结果。

修改后的程序如下：

#include<iostream> 
using namespace std; 

class Base{ 
public: 
    Base(){ 
        a=5;
        cout<<"Base a="<<a<<endl;
    } 
protected: 
    int a; 
}; 

class Base1: public Base{ 
public: 
    int b1; 
    Base1(){ 
        a=a+10;
        cout<<"Base1 a="<<a<<endl;
    } 
}; 

class Base2: public Base{ 
public: 
    int b2; 
    Base2(){ 
        a=a+20;
        cout<<"Base2 a="<<a<<endl;
    } 
}; 

class Derived: public Base1, public Base2{ 
public: 
    int d; 
    Derived(){
        Base1();
        Base2();
        cout<<"Base1::a="<<Base1::a<<endl; 
        cout<<"Base2::a="<<Base2::a<<endl; 
        cout<<"Derived a="<<a<<endl; 
    } 
}; 

int main(){ 
    Derived obj; 
    return 0; 
}

输出结果为：

Base a=5
Base2 a=25
Base1 a=15
Base1::a=15
Base2::a=25
Derived a=15