#include<iostream>
#include<string>
using namespace::std;
string make_plural(size_t ctr, const string &word, const string &ending "s"){
    return(ctr==1)?word:word+ending;
}
int main(){
    cout<<"Singular versior"<<make_plural(1,"success","es")<<
        "\t\tplural version:"
        <<make_plural(0,"success","es")<<endl
        <<"Singular version:"<<make_plural(1,"failue")
        <<"\t\tplural version:"
        <<make_plural(0,"failuue")<<endl;
        return 0;
}

const string &ending="s"

自己实在不知道哪里错了
--- 你编译的时候，编译器肯定给你了明确的错误提示，废话我不讲，你应该这么问

代码如下
（略）
第5行编译错误：error C2143: syntax error : missing ',' before 'string'
请问如何改正？