const成员函数调用的区别！该怎么处理

#include <string>
#include <iostream>
using namespace std;
class Sales_item{
    public:
        int func(Sales_item &si)const;
        int func(Sales_item &si);
        Sales_item():ival(1){
        }
    private:
        int ival;
};
int Sales_item::func(Sales_item &si)const{
    
    return ival;
}
int Sales_item::func(Sales_item &si){
    ival=10;
    return ival;
}
int main(){
    Sales_item si1;
    cout<<si1.func(si1)<<endl;//非const对象调用非const函数
    const Sales_item si2;
    cout<<si2.func(si1)<<endl;//const对象调用const函数
    system("pause");
    return 0;
}