构造do while循环以处理无法使用C ++的帐号

Question

I'm trying to use a do while loop to evaluate account numbers. A valid account number has to have 5 digits and start with the letters R or B, not case sensitive.

Valid account number examples: r90000 B10101 R88888 b77777

invalid account number examples: y90000 r888822

This is the loop I've made, and I can't figure out what's wrong with my parameters that's causing it to repeat over and over again, never excepting an account number.

char accountType;
int accountNum;

cout << "Please enter your account number." <<endl;
cout << ">> ";
cin >> accountType >> accountNum;
cout <<endl;

do 
{
    cout << "That is not a valid account number. Please enter your account number." <<endl;
    cout << ">> ";
    cin >> accountType >> accountNum;
    cout <<endl;
}while ( (accountNum <= 9999) || (accountNum >= 100000) && (accountType != 'r') || (accountType != 'R') || (accountType != 'b') || (accountType != 'B') );

Any ideas?

Answer 1

Your conditions for repeating the loop are any of:

1. accountNum <= 9999
2. accountNum >= 100000 && accountType != 'r'
3. accountType != 'R'
4. accountType != 'b'
5. accountType != 'B'

But for every character, at least two of (3), (4), and (5) are true, so you'll always repeat.

You need to loop while all of the accountType checks fail OR any of the accountNum checks fail. That is, any of:

1. accountNum <= 9999
2. accountNum >= 100000
3. accountType != 'r' && accountType != 'R' && accountType != 'b' && accountType != 'B'