C++ String clear()

str.clear();

#include<iostream>
using namespace std;
int main()
{
stringstr;
cout<<?Enter some lines about lidihuo and write dot character to finish the sentence?<<?\n?;
cout<<?if you want to clear the text, press d?<<?\n?;
do{
charch =cin.get();
str+=ch;
if(ch==?d?)
str.clear();
}while(ch!=?.?);
return 0;
}

Enter some lines about lidihuo and write dot character to finish the sentence
if you want to clear the text, press d