高手大侠请指点迷津

以下程序是我的函授作业，我初学。实在找不出其中错误所在，高手大侠请指点迷津
#include<iostream.h>
class A
{
protected:
int a;
public:
    void SetData(int x) {a=x;}
    int GetData() {return a; }
};
class B
{
protected:
int b;
public:
    void SetData(int y) {b=y;}
    int GetData() {return b; }
};

class C:public A,public B
{
public:
    void SetData(int x, int y) {a=x; b=y;}
};
void main()
{
    C c;
    c.SetData(30,70);
    cout<<"a="<<c.GetData()<<",b="<<c.GetData()<<end1;
}