不可在 for 循环体内修改循环变量，防止 for 循环失去控制

不可在 for 循环体内修改循环变量，防止 for 循环失去控制。

#include <iostream>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */
using namespace std;
//基类
class First {
    int val1;
protected:
    void SetVal1(int v) {
        val1=v;
    }
public:
    show_First(void) {
        cout<<"val1="<<val1<<endl;
    }
};
//派生类
class Second:public First {   
    int val2;
protected:
    void SetVal2(int v) {
        SetVal1(v);  //使用First 基类的保护成员
        val2=v;
    }
public:
    show_Second(void) {
        show_First();
        cout<<"val2="<<val2<<endl;
    }
};
//派生类
class Third:public Second {   
    int val3;
public:
    void SetVal3(int n) {
         SetVal1(n);  //使用First 基类的保护成员
         SetVal2(n);  //使用Second基类的保护成员
         val3=n;
    }
    show_Third(void) {
        show_Second();
        cout<<"val3="<<val3<<endl;
    }
};
//main()函数的定义

int main(int argc, char** argv) {
        First f1;
    //f1.SetVal1(1);   不可访问

    Second s1;
    //s1.SetVal1(1);   不可访问
    //s1.SetVal2(2);   不可访问

    Third  t1;
    //t1.SetVal1(1);   不可访问
    //t1.SetVal2(2);   不可访问
    t1.SetVal3(10);

    //显示t1对象的数据
    cout<<"t1.show_Third();"<<endl;
    t1.show_Third();
    cout<<"t1.show_Second();"<<endl;
    t1.show_Second();
    cout<<"t1.show_First();"<<endl;
    t1.show_First();
    return 0;
}