Mathematical Formula Validator

[pankajit09]

Hi

I want some mechanism to validate a mathematical formula.

For eg: (a+b is not valid since the closing bracket is missing.

Please help.

[ronnil]

you will want to need regular expressions.

start out here http://en.wikipedia.org/wiki/Regular_expression this covers the basics, afterwards you can find the functions working with regular expressions on http://www.php.net/manual/en

[pbmods]

Regular expressions will do the job, though for the sake of your sanity, you'll probably want to use a stack-based parser instead.

Run through your string and push an element every time you encounter an opening parenthesis/bracket. When you encounter a closing parenthesis/bracket, attempt to pop it off the stack. If the stack is empty, or if the next item on the stack doesn't match (e.g., trying to close a parenthesis before closing an inner bracket), you have an invalid string.

[Motoma]

Regular expressions will do the job, though for the sake of your sanity, you'll probably want to use a stack-based parser instead.

Run through your string and push an element every time you encounter an opening parenthesis/bracket. When you encounter a closing parenthesis/bracket, attempt to pop it off the stack. If the stack is empty, or if the next item on the stack doesn't match (e.g., trying to close a parenthesis before closing an inner bracket), you have an invalid string.

If all you are trying to do is check for parenthesis, just use the counting method: ( is +1, ) is -1. If at any point you are negative, you have a bad string. If you are at the end of the string, and you are not 0, you have a bad string.

If you need to do other types of validation, a transformation to polish prefix notation makes numbers quite easy to work with in code.

[pankajit09]

I don't want only for parenthesis.

I want for every case.

[Motoma]

In that case you are going to need to set up a formal document delineating the requirements of your system. Once you have these requirements you can come back if you have issues meeting them.