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();

     //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 ;
 }