(Input validation for multiple cin) is there any way to compress this code?

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I want to add an input validation feature to this program in which the user assigns values to 4 variables. I currently have an if statement after each prompt for the user to enter in a value. Do I have to include this coded after every prompt or is there a way to simplify this? Not urgent, but curious.

int main()
{
	double ux, uy, vx, vy, angle_rad, angle_deg, angle;
	string error = "Error: please enter valid components for the vectors.";
	cout << "Please enter the x-component of vector u: ";
	cin >> ux;
	if (cin.fail())
	{
		cout << endl << error << endl << endl;
		return 1;
	}
	cout << endl << "Please enter the y-component of vector u: ";
	cin >> uy;
	if (cin.fail())
	{
		cout << endl << error << endl << endl;
		return 1;
	}
	cout << endl << "Please enter the x-component of vector v: ";
	cin >> vx;
	if (cin.fail())
	{
		cout << endl << error << endl << endl;
		return 1;
	}
	cout << endl << "Please enter the y-component of vector v: ";
	cin >> vy;
	if (cin.fail())
	{
		cout << endl << error << endl << endl;
		return 1;
	}

What I have tried:

I have tried placing only one string error at the end of all the prompts, however as soon as an invalid input is received, it will still show the other cout displays before displaying the string error.

Posted 19-Sep-16 17:09pm

y0ung_chuck

Updated 19-Sep-16 21:34pm

CPallini

v2

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Peter_in_2780 20-Sep-16 2:08am

Looks very much like a case for a subroutine.

2 solutions

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Jochen Arndt · Answer 1 · 2016-09-19T21:17:00

If you want to break upon an invalid input you have to check a condition at each input. But you can use a function for each input that prints the error message:

C++

#include <float.h>

bool getDouble(double &val, const char *msg, double min = DBL_MIN, double max = DBL_MAX)
{
    bool bValid = true;
    cout << endl << msg;
    cin >> val;
    if (cin.fail())
    {
        cout << endl << "Error: please enter valid components for the vectors." << endl << endl;
        bValid = false;
    }
    else if (val < min)
    {
        cout << endl << "Error: Value is too small" << endl << endl;
        bValid = false;
    }
    else if (val > max)
    {
        cout << endl << "Error: Value is too large" << endl << endl;
        bValid = false;
    }
    return bValid;
}
</float.h>

Then call this function for each input:

C++

if (!getDouble(ux, "Please enter the x-component of vector u: "))
    return 1;
if (!getDouble(uy, "Please enter the y-component of vector u: "))
    return 1;
// ...

CPallini · Answer 2 · 2016-09-19T21:34:00

Solution 2

Also note there is room for some OOP in your scenario. You could define a bidimensional vector class and overload the input (and possibly) output operators for it.

Posted 19-Sep-16 21:34pm