Why would we call cin.clear() and cin.ignore() after reading input?
c++, cin, input, iostream
Solution
The `cin.clear()` clears the error flag on `cin` (so that future I/O operations will work correctly), and then `cin.ignore(10000, '\n')` skips to the next newline (to ignore anything else on the same line as the non-number so that it does not cause another parse failure). It will only skip up to 10000 characters, so the code is assuming the user will not put in a very long, invalid line.
Problem
Google Code University's C++ tutorial used to have this code: ``` // Description: Illustrate the use of cin to get input // and how to recover from errors. #include <iostream> using namespace std; int main() { int input_var = 0; // Enter the do while loop and stay there until either // a non-numeric is entered, or -1 is entered. Note that // cin will accept any integer, 4, 40, 400, etc. do { cout << "Enter a number (-1 = quit): "; // The following line accepts input from the keyboard into // variable input_var. // cin returns false if an input operation fails, that is, if // something other than an int (the type of input_var) is entered. if (!(cin >> input_var)) { cout << "Please enter numbers only." << endl; cin.clear(); cin.ignore(10000,'\n'); } if (input_var != -1) { cout << "You entered " << input_var << endl; } } while (input_var != -1); cout << "All done." << endl; return 0; } ``` What is the significance of `cin.clear()` and `cin.ignore()`? Why are the `10000` and `\n` parameters necessary?