input validation using isalpha and isdigit?

[jpanther]

Hello everyone, I am trying to validate the user input by using isalpha and isdigit. The input is supposed to consist of the following format: AB123456. I was going to check for AB using isalpha and 123456 using isdigit. The input needs to consist of two letters and six numbers. I was also going to assign the input to an array so I could check it.

This is my first time using these, so I'm not too sure how to implement it into my code. I know how to validate an input that is all characters or all digits, but not if it's a combination of the two.

Here is what I got. It doesn't compile. Can someone point me in the right direction? Thank you:

void searchID ()
{
 //local variable
 string userInput;
 int count = 0;
 
 do
 {
  cout << endl << "Enter ID number of student to find (or X to exit): ";
  cin >> userInput;
     while((isalpha(userInput[0])) || (isalpha(userInput[1])) ||  (isdigit(userInput[2])) || (isdigit(userInput[3])) || (isdigit(userInput[4])) || (isdigit(userInput[5])) || (isdigit(userInput[6])) || (isdigit(userInput[7])))                      
         {
            cout << "Invalid entry. Try again." << endl;
            cin >> userInput; 
         }
        if (userInput == 'X')
  {
   cout << "Goodbye!" << endl << endl;
   system ("PAUSE");
  }
 }while (userInput != 'X')
 
 return;
}

[Guest]

Using a while loop for the verification looks like a mistake to me. You enter the ID and then you want to verify its format, so an if would be a better choice.

It would suggest you create a validation function separate from the input handling. Something like:

bool isValid(const string& id)
{
    return (isalpha(id[0]) && isalpha(id[1]) && isdigit(id[2]) ...etc);
}

[jimblumberg]

Have you considered using one or two of the string.find() series of functions instead of the isalpha() and isdigit() (ie: std::string.find_first_not_of())?

Jim

[cstryx]

Since this is not an array of a predefined length as far as the std::string typedef is concerned, before just indexing a bunch of random char's, you may consider checking the length() for safety too.

if (str.length() != 8) return false;

This could be part of the check as well as for safety with the indexing operator, being that if the string length is not 8, there can't be 2 letters and 6 digits in the string.