problem with simple error checking

As far as isnumber() goes, I made a mistake. Apparently isnumber() is also a function because it didn't raise an error, but it was a typo -- the function I meant to use was isdigit(), not isnumber(). So, I changed the function isnumber() to isdigit(), but still got the exact same result.

I've since figured out what the problem is, though. The function isdigit() was given in the notes my professor provided, along with isalpha(), ispunct(), isspace(), isupper(), and islower(). It occurred to me that these functions are intended to be used with single characters, and in my code I had defined the variable input as an int. So, I changed input to data type char and it worked fine.

So, that solves that issue, but raises another. Consider the following code, if you will:

int numHands;
while (numHands < 1 || numHands > 7)
{
 cout << endl << "How many hands do you want to play: ";
 cin >> numHands;
 
 if (numHands < 1)
 {
 cout << endl << "You must play at least one hand...";
 wait();
 }
 else if (numHands > 7)
 {
 cout << endl << "You can not play more than seven hands...";
 wait();
 }
}

This is a simple bit of error checking to make sure that the number that the user enters is between 1 and 7, and in that regard, it works fine. It does not, however, ensure that what the user enters is a number in the first place. My original solution to this was the following code:

while (numHands < 1 || numHands > 7 || isdigit(numHands) == 0)
{
 cout << endl << "How many hands do you want to play: ";
 cin >> numHands;
 
 if (numHands < 1)
 {
 cout << endl << "You must play at least one hand...";
 }
 else if (numHands > 7)
 {
 cout << endl << "You can not play more than seven hands...";
 }
 else if (isdigit(numHands) == 0)
 {
 cout << endl << "You did not enter a number...";
 }
}

When this didn't work, it prompted me to post this thread, but as I mentioned at the beginning of this post, I realized that the reason it didn't work was because isdigit() works with char and not int data types, and I obviously can't declare numHands as a char because the user could enter more than one character as input.

How, then, can I error check to ensure that the user's input is, in fact, a number?

Okay. Interesting. I played around with that some. I tried incorporating it into my code, but after the first iteration I wasn't allowed to re-enter my input, so I gave up.

Anyways, out of curiosity, how come, in the code below, an error isn't raised when I attempt to store the value 'a' in an int variable?

int input;
cout << "Enter a number: ";
cin >> input;

If I enter a non-numerical value here, like 'a', how come I don't get a runtime error? I was thinking maybe its ASCII value was assigned to the int variable or something, but I can enter a whole string of characters and I still get no error. I found this surprising.

Okay, that makes sense. Thank you.

Also, I played with the code you gave with the if statement using cin as the condition, and bumped into an issue.

int input;
cout << "Enter a number: ";
cin >> input;
if (!cin)
{
 cout << endl << "You did not enter a number."
 << endl << "Enter a number: ";
 cin >> input; // problem here
}

The code works in the sense that if I enter a numerical value, the test fails and the program terminates as it should, and if I enter a non-numerical value, I get the error message just like I should. So that's all good. It works as far as testing whether or not a numerical value was entered goes. The problem comes with the next input statement inside the if structure. After the "You did not enter a number" error message, "Enter a number: " is displayed on the next line, like it should be, except the program terminates then and there. I can't enter any input after the "Enter a number: " line because the program terminates. It's as if the second +cin >> input;+ statement (the one inside the if structure) is being ignored all together. The program displays the two lines of text from the cout statement inside the if structure and immediately terminates. Can you offer any insight?

I looked into the book you recommended. It looks like I could learn a lot from it, although it's a bit on the expensive side. Hopefully I'll be able to afford it sooner or later -- it looks good.

By the way, the clear() method you mentioned -- do I need to #include something for it to work, because I'm getting an error when I try to use it ("error: 'clear' was not declared in this scope")?

Okay. Thanks, et.