The following code goes on a loop when I input a letter, how can I stop the loop using exceptions in C++

_#include

_#include

_{using namespace std;}

_{const double centimeterToInches = 2.54;}

_{const int footToInches = 12;}

_{int main()}

_{

_{int feet;}

_{int inches;}

_{int totalInches;}

_{double centimetre;}

_{bool done = false;}

_{string negativeInput = "Invalid... Do not enter negative or non-digit numbers, Please enter another set of numbers";}

_do

_{

_try

_{

_{cout << "Enter the length in feet: ";}

_{cin >> feet;}

_{if (feet <= 0)}

_{throw negativeInput;}

_{cout << "enter the length in inches: ";}

_{cin >> inches;}

_{if (inches <= 0)}

_{throw negativeInput;}

_{else if (isalpha(feet) != 0 || isalpha(inches) != 0)}

_{throw negativeInput;}

_{done = true;}

_{totalInches = footToInches*feet + inches;}

_{centimetre = centimeterToInches*totalInches;}

_{cout << "The length in centimeters is:" << centimetre << endl;}

_}

_{catch (string inputerror)}

_{

_{cout << inputerror << endl;}

_cin.clear();

_}

_{} while (!done);}

_{return 0;}

_}