类对象出错

#include <iostream>
using namespace std;
    class A
    {
        
    int x,y;
    public:
        A()
        {
            x = 0;
            y = 0;
        }
        A(int i = 1, int j = 0)
        {
            x = i;
            y = j;    
        }
        void show()
        {
            cout << x << ',' << y <<endl;
        }
    };

int main()
{
    A a1 ;                     //编译器告诉我这里call指向模糊不清，我看书上也是这么写的，哪位高手能解释一下
    A a2(3,6);
    a1.show();
    a2.show();
    return 0;
}