>>69
#include <iostream>
#include <string>
using namespace std;
void catstring(char const* s1,char const* s2="お疲れさん"){
  cout << s1 << s2 << endl;
}

int main(void) {
  string s1,s2;
  cout << "Input string1";
  cin >> s1;
  cout << "Input string2";
  cin >> s2;

  catstring(s1.c_str());
  catstring(s1.c_str(),s2.c_str());
}