下列程序编译错误，是由于划线处缺少某个语句，该语句是______。
include＜iostream.h＞
class A
{
private:
int numl;
public:
A( ):numl(0){}
A(int i):numl(i){}
};
class B
{
private:
int num2;
public:
B( ):num2(0){}
B(int i):num2(i){}
int my_math(A obj1, B obj2);
};
int B::my_math(A obj1,B obj2)
{
return(obj1.numl+obj2.num2);
}
void main(void)
{
A objl(4);
B obj,obj2(5);
cout＜＜"obj1+obj2:"＜＜obj.my_math(obj1,obj2);
}