Exception Handling: stuck in infinite loop if a char is entered - c++

Question

I'm having a problem with my exception handling. It seems to work with negative input, but whenever I try to enter a character, it gets stuck in an infinite loop in the first try/catch block.
I try clear() and ignore() for cin, but it still didn't work. I tried a different if statement for input, such as (if ((ft >100)) || (in >100)), and the exception is thrown just fine.
Am I missing something?
#include <iostream>
using namespace std;
class convert
{
private:
int feet;
int inch;
public:
convert() = default;
double calculation(int ft, int in)
{
double cm = 0;
cm = ((ft * 30.48) + (in * 2.54));
return cm;
}
};
class negativeNumber
{};
class invalidInput
{};
int main()
{
int ft;
int in;
double cm = 0;
convert h;
while (true)
{
try
{
cout << "Please enter your height in (ft, in) format" << endl;
cin >> ft;
cin >> in;
if ((ft < 0) || (in < 0))
{
throw negativeNumber();
}
if (cin.fail())
{
throw invalidInput();
}
cm = h.calculation(ft, in);
cout << "Your height in cm is: " << cm << endl;
break;
}
catch (negativeNumber)
{
cout << "You entered negative numbers. Try again" << endl;
system("pause");
}
catch (invalidInput)
{
cout << "You entered a character. Try again" << endl;
system("pause");
}
}
return 0;
}

Answer 1

You absolutely need to call cin.clear() and cin.ignore() when input fails to read. You need to clear cin's error state in order to continue reading input, and you need to remove the failed data from cin's input buffer so you don't keep reading the same data over and over.
Also, you should check for input failure before checking for negatives. ft and in will not have valid values if they fail to read.
Also, you should always catch exceptions by (const) reference, not by value.
Try this instead:
#include <iostream>
#include <limits>
using namespace std;
class convert
{
public:
static double calculation(int ft, int in)
{
double cm = 0;
cm = ((ft * 30.48) + (in * 2.54));
return cm;
}
};
class negativeNumber
{};
class invalidInput
{};
int main()
{
int ft;
int in;
double cm;
while (true)
{
try
{
cout << "Please enter your height in (ft, in) format" << endl;
if (!(cin >> ft >> in))
{
throw invalidInput();
}
if ((ft < 0) || (in < 0))
{
throw negativeNumber();
}
cm = convert::calculation(ft, in);
cout << "Your height in cm is: " << cm << endl;
break;
}
catch (const negativeNumber &)
{
cout << "You entered a negative number. Try again" << endl;
system("pause");
}
catch (const invalidInput &)
{
cout << "You entered bad input. Try again" << endl;
cin.clear();
cin.ignore(numeric_limits<streamsize>::max(), '\n');
system("pause");
}
}
return 0;
}