要主函数吗？

#include <iostream.h>
                                                     //要主函数吗？
class A{
private:
     int x,y;
public:
     void ask1(int a=0,int b=0);
     int ask2();
     void ask3();
};
void A::ask1(int a,int b){x=a;y=b;}
int A::ask2()
{
     if(x>y)
     {
          return (x);
     }
     else return (y);
}
void A::ask3()
{
     cout<<x<<endl<<y<<endl;
}


--------------------Configuration: Cpp3 - Win32 Debug--------------------
Compiling...
Cpp3.cpp
Linking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/Cpp3.exe : fatal error LNK1120: 1 unresolved externals
执行 link.exe 时出错.
Cpp3.exe - 1 error(s), 0 warning(s)


是什么意思吖`？？

[[italic] 本帖最后由 heluhui123 于 2007-12-5 15:13 编辑 [/italic]]