Input Validation

[Lab]

New to programming(just a few weeks into it) and 1st forum ever joined so bare with me while I go thru the learning curve on how forums work.

Assignment is as follows:

Write a program that will ask a user to enter the current Tempeature
(-50 to 50,decimal), windspeed(3 to 150, whole number) and ask whether
thier input was in Fahrenheit or Celcius(f or c). It should then
echo the temperature and wind speed entered in BOTH Fahrenheit and Celcius
(to 1 decimal place) and output the wind chill in BOTH Fahrenheit and Celcius.
(to 1 decimal place).

I wrote it using an example the instructor showed in class as follows:
(only part of code)

Question: How do I validate only a number is entered?

		do// loop to test valid windspeed entered.
			{      
			cout << "Enter Wind speed (3 to 150):";
			cin >> windspeed;

			if ((windspeed < 3) || (windspeed > 150))
				{
				cout << "Please re enter a windspeed"
					<< " between 3 and 150:";
				cin >> windspeed;
				}
			else
				wsFlag = true;
			}while (wsFlag != true);// end windspeed validation loop.

the problem is if a charachter is entered rather than a number the programm goes crazy to say the least

I thought I saw a previous post relating to this but cannot find it again!!
Thank you all

[R-G]

I think, with an similar example of a source software code algorithm, written in the computer programming language C++ you will understand it better.

while (!Valid)
    {
        cout << "Enter a number string: ";
        cin >> Number;
        if (cin)
        {
            cin.ignore(numeric_limits<int>::max(), '\n');
            if (cin.gcount() == +1)
            {
                if ( Number >= 0)
                {
                    Valid = true;
                }
            }
        }
        else
        {
            cin.clear();
            cin.ignore(numeric_limits<int>::max(), '\n');
            cout << "Not a valid number string. Try again: \n";
        }
    }

[WingedPanther]

Generally, accepting your input as a string and then determining if it represents a number is safer than requiring the input to be a number.

[Xav]

Why is that? Are there disadvantages of validating the input first?

[mholt]

Maybe.... there is one way that I know of that works pretty well... but if they make a mistake, Backspace won't help them:

Try the C function getch():

// Be sure to include conio.h
// This function returns a string
// of only numbers, validated
// as typed.

string EnterOnlyNumbers() {
	string numString = "";
	char ch = getch();
	while (ch != '\r') { // \r is the enter key
		if (ch >= '0' && ch <= '9') {
			cout << ch;
			numString += ch;
		}
		ch = getch();
	}
	return numString;
}

If you modify it a little bit, you can use this code for password input, so the password will not be displayed on the screen. (Print out "*" instead of ch.)

However, my compiler gives me warnings on the getch() function, probably because it is indeed depreciated. If you want the best code, getline() as a string then validate it.

[Xav]

Thanks - if you just want a character, then I suppose it's easy enough just to get the whole line, then parse out the character required.

[dcs]

Ignoring all characters - Dev Shed