金玟贞电影:C++编程问题

#include<iostream.h>
class vehicle
{
public:
vehicle(int x,float y)
{
wheels=x;
weight=y;
}
void print()
{cout<<"qichegeshu"<<wheels<<"qichechezhong"<<weight<<endl;}
protected:
int wheels;
float weight;
};
class car: protected vehicle
{
public:
car() //问题在这里报错
{cin>>passenger_load;}
void print()
{
vehicle::print();
cout<<"xiaoqicherenshu"<<passenger_load<<endl;
}

protected:
int passenger_load;
};
class truck:protected vehicle
{
public:
truck()
{cin>>passenger_load>>payload;}
void print()
{
cout<<"kacherenshu"<<passenger_load<<"kachezhongliang"<<payload<<endl;
}
protected:
int passenger_load;
float payload;
};
void main()
{ int x;
float y;
cin>>x>>y;
vehicle a(x,y);
car b;
truck c;
c.print();
b.print();
}

car()这里会报错说
'vehicle' : no appropriate default constructor available
请问这是意思？我看了半天书。书上格式和我打的一样。为什么会报错呢？
这个是我自己编的。不是按书上打的。只有格式是按书上对着打。请高手帮忙看看是什么问题。软件我是从猪猪乐园下的。中文版创天。