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Exception Handling of tokens

kanaka tam
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Joined: Jan 19, 2004
Posts: 42
Hi folks,
I have written an application that acts like a simple calculator and performs addition or subtraction of numbers entered in a certain pattern. I was successful in writing the program and compiling it and exceuting it. I am having little bit of trouble in handling exceptions.
I have to handle four kinds of errors and i did get 1 and 3. But didnt know how to achieve 2 and 4.
1. No input at all. The user presses �calculate� and the input text field has nothing to calculate. Put the message, �Enter An Expression� in the top text field if this occurs (and make the bottom text field blank.
2. Wrong number of operators and operands. There should always be an odd number of items (�55� is one instance, � 3 + 2� is three, etc.) Report �Wrong Number Of Elements� in the bottom text field if there is not an odd number of elements (after you tokenize on �+� and �-� ).
3. Invalid operand. If you find something that is not a valid operand (i.e., not an integer) in a place where you would expect an operand to be, then leave the user�s expression in the top text field and put the message �Invalid Operand Or Operator� in the bottom text field.
4. Invalid operator. If you find something that is not a valid operator (i.e., not a �+� or a �-�) in a place where you would expect to find an operator, then leave the user�s expression in the top text field and put the message �Invalid Operand Or Operator� in the bottom text field.
Below is my code:

My code handles the follwing exceptions.
When the user fails to enter any value and presses calculate, A message "Enter an Expression" appears in the input text field. if the user enters say "12 - a" i display a message invalid operand.
But my code does not catch an exception like say "12 & 2" then i should display invalid operator and also a message wrong number of elements if the user enters "12 - ". Any help would be greatly appreciated.
Thank you,
kt
[ July 30, 2005: Message edited by: kanaka tam ]
 
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subject: Exception Handling of tokens
 
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