check for bad input

[tcs122499]

I have an integer variable that that I need to check if someone enters only integers. I have the following code but if they enter something such as "dfgdsfdsfdsf" but it goes into an infinite loop and doesnt wait for the user to input data again. The variable guess is the variable that is an integer and cannot accept characters. The following is what I have so far:

rndNbr = randomNbr(); //Generate a random number

cout << "I have a number between 1 and 1000.\n";
cout << "Can you guess my number?\n";
cout << "Please type your first guess.";

do
{
if(!(cin >> guess)||(guess > 1000)||(guess < 1))
{
cin.clear();
cout << "\n" << "Not between 1 and 1000! Try again.\n";
}
}
while((guess > 1000)||(guess < 1));

[Cela]

There are a bunch of ways to validate input, but one thing you have to remember to do if cin fails is clear the stream and discard the bad stuff. Since a failed call to cin doesn't read the bad stuff, you're stuck with it until you throw it away :-)

#include <iostream>

using namespace std;

int getInt()
{
  int ret;

  if (!(cin>> ret) || ret < 1 || ret > 1000)
  {
    // Not good, but let the caller recover
    throw 1;
  }

  return ret; // It's good
}

int main()
{
  while (true)
  {
    try
    {
      cout<<"Enter a number: ";
      cout<<"Your number is "<< getInt() <<endl;
    }
    catch(int)
    {
      cout<<"Invalid input"<<endl;
      cin.clear(); // Clear the stream
      while (cin.get() != '\n')
      {} // Discard bad stuff
    }
  }
}

[newbie_grg]

you could use isdigit(guess) if i am not wrong.
it checks if the entered number is digit.

[newbie_grg]

you could use isdigit(guess) if i am not wrong.
it checks if the entered value is digit.

[PJYelton]

isdigit() only works for chars.

[newbie_grg]

i guess it also works for string.

[Cela]

>>i guess it also works for string.
Only characters in the string, not whole strings though :-)

[alpha]

Originally posted by PJYelton
isdigit() only works for chars.

isdigit() actually takes an int.

[PJYelton]

Ok, it does take an int, but its meant to see if a char is in the ASCII range of '0'-'9'. So isdigit(5) will return false even though 5 is a number.

[DougDbug]

I'm not going to give an example, 'cause all of my programs here at work are in C (Yuch!). But, I almost always offer the user a default entry. So, if the user simply presses [ENTER], or enters something invalid, he/she gets the default. (I also usually report-back that the default is being used.)

So, my prompts might be something like these:

cout << "Number of channels to test (1-4) [4] " << endl ;

cout << "Test #2 ***FAILED*** Continue? Y/N [Y] " << endl ;

In the first case, if the user enters anything other than 1 thru 4, the program will behave as if he/she entered 4. In the second case, anything other than an upper or lower case "N", and the program will assume "Yes".

In this way, our programs "work" no matter what the user enters... just maybe not doing what the user intended.