字符反转递归方法c++

#include<iostream>
#include<string>


using namespace std;
int main()
{
string a;
cin>>a;
string contrarystr(string);
   cout<<contrarystr(a);
return 0;
}
string contrarystr(string a)
{
if(a.length()<=1) return a;
return contrarystr(a.substr(1,a.length()-1))+a[0];
}