怎么给引用类型的参数指定默认值？

C/C++ code

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string make_plural(int t,const string &word,const string &ending="s");
    string str="apple";
    cout<<make_plural(1,str);
    return 0;
}
string make_plural(int t,const string &word,const stirng &ending="s")
{
    return (t==1)? word:word+ending;
}

C:\Users\admin\Documents\1212.cpp|11|error: ISO C++ forbids declaration of 'stirng' with no type|
C:\Users\admin\Documents\1212.cpp|11|error: expected ',' or '...' before '&' token|
C:\Users\admin\Documents\1212.cpp||In function 'std::string make_plural(int, const std::string&, int)':|
C:\Users\admin\Documents\1212.cpp|13|error: 'ending' was not declared in this scope|
||=== Build finished: 3 errors, 0 warnings ===|


这个是用来求单词的复数形式，我想给ending指定一个默认的s

string写错误了
string make_plural(int t,const string &word,const stirng &ending="s")
应为
string make_plural(int t,const string &word,const string &ending="s")