[Resolved] Input valid data?

[The Hobo]

How can you prevent errors from occuring when a user inputs wrong information? Lets say I ask for an integer value (like below) and they put 'a'? It then causes a major spaz in the program.

Example Code:

#include <iostream>
using namespace std;

int main() {
    
    int num;

    cout << "Enter an Integer: ";
    cin >> num;
    
    while (num < 1 || num > 5) {
        system("CLS");
        cout << "Enter an INTEGER: ";
        cin >> num;
    }

    cout << endl << num << endl << endl;

    return 0;
}

How can this be prevented?

[parksie]

#include <iostream>
#include <vector>
#include <iterator>

using namespace std;

int main() {
	cout << "Please enter some numbers, end with -1: " << flush;

	vector<int> nums;
	int num = 0;

	while(!cin.eof()) {
		cin >> num;

		if(num == -1 || cin.fail()) {
			// stop when we get either -1 or something
			// that wasn't recognised as a number
			break;
		}

		nums.push_back(num);
	}

	cout << endl << "You entered:" << endl;

	copy(nums.begin(), nums.end(), ostream_iterator<int>(cout, "\n"));

	cout << endl;

	return 0;
}

This uses cin.fail() to check whether the input actually worked or not.

[The Hobo]

I'm not sure I follow that code...

What I'm trying to do is have a menu in which the user chooses 1 through 5. It's easy enough to make sure it's between 1 and 5, but I need to prevent 5.5, a, +, etc because it makes the program spaz.

That code just confuses me.

[parksie]

Try and read an integer. Then call cin.fail(). If it returns true, then it didn't work.

Run the code, see what it does, look in a debugger. It's very simple

[The Hobo]

Originally posted by parksie
Try and read an integer. Then call cin.fail(). If it returns true, then it didn't work.

Run the code, see what it does, look in a debugger. It's very simple

I tried calling cin.fail() after reading an integer:

#include <iostream>
using namespace std;

int main() {
    
    int num;

    cout << "Enter an Integer: ";
    cin >> num;
    
    while (num < 1 || num > 5 || cin.fail()) {
        system("CLS");
        cout << "Enter an INTEGER: ";
        cin >> num;
    }

    cout << endl << num << endl << endl;

    return 0;
}

Still goes crazy.

[CornedBee]

while (num < 1 || num > 5 || cin.fail()) {
        cin.clear();
        system("CLS");
        cout << "Enter an INTEGER: ";
        cin >> num;
    }

cin won't read again until you clear the status.

[parksie]

[mike@relativity junk]$ ./hobo
Enter an Integer: 10
sh: CLS: command not found
Enter an INTEGER: -4
sh: CLS: command not found
Enter an INTEGER: 4.3

4

[mike@relativity junk]$

...acts like I'd expect it to, I think. I made a fix to stop it going mental if you added a letter:

#include <iostream>
#include <cstdlib>

using namespace std;

int main() {
    
    int num;

    cout << "Enter an Integer: ";
    cin >> num;
    
    while (num < 1 || num > 5 || cin.fail()) {
        cin.clear();
        cin.ignore();

        system("CLS");
        cout << "Enter an INTEGER: ";
        cin >> num;
    }

    cout << endl << num << endl << endl;

    return 0;
}

It's the .clear() and .ignore() -- the clear() resets the fail status, and the ignore() tells it to move past the offending character (the one you gave). So far this means that it'll give enough errors for each character you give it.

I'll let you work that out though

[CornedBee]

parksies test shows another interesting thing...
But I admit I know of no solution.

[parksie]

Solution is to use getline, and parse it yourself.

[CornedBee]

I actually mean this:
sh: CLS: command not found



Interesting, when just viewing posts mine is after yours. When replying it is before yours.

[parksie]

That's because I think it needs "cls" not "CLS"...perhaps.


Nope..."clear" on a terminal

[CornedBee]

system is bound to be platform-dependent. Except cd, but this is quite useless.

[The Hobo]

Damn...I was hoping for short and sweet, but this seems like too much.

[parksie]

Heh, there's never any "short and sweet"

[Zaei]

Originally posted by parksie
Heh, there's never any "short and sweet"

Actually, Its called VB =P.

Z.

[CornedBee]

Sweet?

[Zaei]

Good, like candy =).

Z.

[parksie]

Yeah, but it's completely non-portable

[CornedBee]

VB is like candy. Sweet and nice, but it'll ruin your teeth and you won't be able to chew on hard problems anymore

[Zaei]

Originally posted by parksie
Yeah, but it's completely non-portable

[n00b]
What r u talking about? I can put vb progs on Windows 95, and 98, and Xp, and ME, and 2000!!!
[/n00b]

Z.

[parksie]

=)

[Zaei]

Nice smiley you got there =).

Z.

[kedaman]

VB is going to be quite useless when SQ comes out =)

[The Hobo]

Hey, dude. Don't break my watermelon because I'm all punch, y'see?

I don't know what I said either...

[transcendental]

Originally posted by kedaman
VB is going to be quite useless when SQ comes out =)

What's SQ?

[CornedBee]

SQ stands short for Squirrel, which is a language Keda has developed, which follows none of the current programming paradigms (function-oriented, object-oriented, etc). Click at the link in his sig for a very confusing explanation of it.

[Zaei]

Its not confusing to kedaman...
But he isnt human =P

Z.

[CornedBee]

I have this impression too sometimes...

I'm always terribly confused, but not as confused as when I see the syntax definition (same location).

[MoMad]

Hey man, have you tried this:

int num;
char ch = 0;

do {
        system("cls");
        cout << "Enter an INTEGER: ";
        cin >> ch;
        cin.ignore ();
} while (ch < '1' ||  ch > '5');

num = (int) ch - '0'; 

How hard could that be

[The Hobo]

Actually, yes.

cin >> option;

while (option < '1' || option > '5') {
    system("CLS");
    cout << "Try again!" << endl << endl;
    cout << "Please choose a number (1) through (5): ";
    cin >> option;
}

choice = option - 48;

is what I did.