unresolved external symbol "public: __thiscall cat //错误

:#include <iostream>

using namespace std;

class cat
{ public:
cat(int age){itsage=age;}

~cat();
int getage()const {return itsage;}
private:
int itsage;
};

cat *makecat(int age);

int main()
{

int age=7;
cat * boots=makecat(age);

cout<<"boot is"<<boots->getage()<<"old"<<endl;

delete boots;
return 0;

}

cat *makecat(int age)
{ return new cat(age);

}

新手上路，大家帮我看看是哪里的问题。下面是显示的错误
error LNK2001: unresolved external symbol "public: __thiscall cat::~cat(void)" (??1cat@@QAE@XZ)
Debug/4.exe : fatal error LNK1120: 1 unresolved externals这里专家的回答会让您满意

~cat();
变成
~cat(){}