Formula Validation

[pankajit09]

Hello,

I have a expression like this -->

(a+b/c)

How to validate it ?

For eg: if the expression is (a+b/c then error should be thrown.

[Markus]

Hello,

I have a expression like this -->

(a+b/c)

How to validate it ?

For eg: if the expression is (a+b/c then error should be thrown.

I dont understand.
How would the user give you the formula?

[pankajit09]

I dont understand.
How would the user give you the formula?

The user will enter the formula in a textbox which is present in a form.

[aktar]

Try this:

in your code will be :[PHP]$a = [the value];
$b = [the value];
$c= [the value];

$correct_answer = [the correct answer];[/PHP]now you can convert the formula text you receive from the user, like so:[PHP]($a+$b)/$c[/PHP]
then you can use a fuction like eval() to calculate a value based on the users input. Then its just a matter of matching it with the $correct_answer

like so:[PHP]eval('$user_answer = ($a+$b)/$c;');

if ($user_answer != $correct_answer){

//TRHOW ERROR!!!

}[/PHP]Regards

[TheServant]

If users are writing their own functions then you will need a lot of searching and counting in the strings, so before I spend time on that tell me if it's a set formula or not. If it is aktar's code looks good!

[pankajit09]

If users are writing their own functions then you will need a lot of searching and counting in the strings, so before I spend time on that tell me if it's a set formula or not. If it is aktar's code looks good!

The formula will be limited to BODMAS like (x+y)/z

I just want to validate it .

[TheServant]

The formula will be limited to BODMAS like (x+y)/z
I just want to validate it .

So a user could enter something like x+(y*z)/2+y*x???

If so, this is complicated, and I am about to go home. Please confirm this is the case, because if users can enter their own formulae it means that you need to make lots and lots of rules to test each string by, and no point in wasting time on it if I have misunderstood.

[pankajit09]

So a user could enter something like x+(y*z)/2+y*x???

If so, this is complicated, and I am about to go home. Please confirm this is the case, because if users can enter their own formulae it means that you need to make lots and lots of rules to test each string by, and no point in wasting time on it if I have misunderstood.

yes you are right.

Has someone did it ?

[dlite922]

yes you are right.

Has someone did it ?

BODMAS excercises?

http://www.abacustraining.biz/bodmasExercises.htm

What is an example of what the user exactly entering...

This:

3*2(2+4/2)-13

OR

This:

x+y(z-z*2)/k

are you verifing the "syntax", IOW making sure the parenthesis are matched up and return a true or false,

or do you need to calculate the expression and give the a number result? or perhaps compare it with your number to see if correct?

If you're looking for the first example, then all you need to do is search for parenthesis. count all the left parenthesis and count all the right parenthesis, if the numbers don't match, they left a parenthesis out and their syntax is incorrect.

if second example, then use eval();
if using eval() BE VERY CAREFUL to filter the content, otherwise i can execute any PHP code on your Site!!

for example, use regex to check for characters other than -,+,*,/ 0-9 and a-z;

no semi-colon in content given to eval() should make it a litte safer. maybe user str_replace() and replace all semi-colons with an empty string.

Good luck,


Dan