another quick question

[koopa]

hi,

easy one, i hope, in a simple program, where the user is requested to input a number (stored as an int), if the user accidentally inputs a letter the console crashes instantly, how would I prevent the prog from crashing if a letter was accidentally entered intead of an int?
I'm using visual C++ express 2008.

Thanks.

[jsmith]

You will need to check the stream for errors after your cin >> num;, otherwise
you don't know if num was filled out successfully.

[koopa]

thanks for the response, how does one check the stream for errors?
could you give me an example?

[spaggy]

http://www.cplusplus.com/reference/iostream/ios/good/
http://www.cplusplus.com/reference/iostream/ios/bad/

[koopa]

thanks spaggy, but how do I implement this? forgive me I am very fresh to C++, the bool good(); looks like it will do the job alright, how would I implement this in the code?

e.g.
int number;
cout << "please enter a number" << endl;
cin >> number;

how do I implement bool good() here as to flag if a letter is incorrectly entered as an int?

thanks.

[spaggy]

cin is an istream so good is a member of cin.

so right after cin >> number, check the value of cin.good().

Sort of like

if(cin.good())
{
//do stuff as normal
}
else
{
//print an error or something
}

[koopa]

Ok tried this in a quick test (code below) and it still fails, compiles fine but when I enter a letter the console screen crashes (loops continuously)? Have I implemented this correctly? whould this detect the error in a letter being entered?

	//test
	cout << endl << "please enter a number " << endl;
	int number;
	cin >> number;

	if (cin.good())
	{
		cout << endl << number << endl;
	}
	else
		cout << "you need to enter a number" << endl;
	
}

[koopa]

Hi all,

quick update, the above code actually works ok if I run one time, however if I try to loop and request a number a second time ot continually loops (doesnt seem to execute the cin again.

I have written some simple code below (probably over complex), the intent here is to request an input number, check that a number is input (if a letter instead of a number is input it should request a number again). Now when this code is executed it works of for a number but when I input a letter it just loops without again prompting for a number? Can anyone explain why this is?
Thanks.

#include <iostream>
using namespace std;
bool test();
int main()
{
	test();
	while (test()== false)
	{
		test();
	}

	return 0;
}

bool test()
{
	unsigned short int number;
	cout << "please enter a number " << endl;
		cin >> number;

		if (cin.good())
		{
			cout << number << endl;
			return true;	
		}
		else
			cout << "you need to enter a number" << endl;	
			cin.clear();
			return false;
}

[koopa]

hi,

sussed it!

needed a cin.sync() post the cin.clear()