VALIDATING INPUT

Here is a good way to validate numeric input.
(Other useful methods in JAVA book, page 51.)
boolean inputOK = false;
while (!inputOK) // loop repeats until input is valid
  { if ( isValid(Xfield) )
        { x = getNumber(Xfield);
          inputOK = true;
        }
        else
        { messageBox ("Input must be an integer.");
          }
  } // end of loop

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