To read from cin, use a std::string.
Then you don't have to guess how big your buffer should be.
cin >> input;
cout << intput;
If you need a C-style array you can do:
const char* cstyle = input.c_str();
To signify the conclusion of a C-style string, the last character is invariably the null terminator '0'.
It is critical to understand when your character sequence stops.
char* text = "hello"; // the compiler puts an extra '\0' at the end
std::string str("hello"); // does not have a null terminator! (before C++11)
str.c_str(); // this returns "hello\0" with a null terminator