math question

FrozNic

let's say i have a text box
i put in 5+5= as the value
is there a function that will take text in a text box and treat it as a math equation? any thougts?

i'm afraid i'm going thave to make a huge string function to pull values out and put stuff in an array and calculate each value and do the operation manually.. i don't want to reinvent it if i don't have to cuz it's going to take a lot of time. any ideas? thanks

DeltaRho2K

I have not specifically seen any prewritten functions to do this... You are probably going to have to reinvent the wheel on this one... Oh well, there's something to be said for this world's pioneers ;-)

erikwebb

i have never used this myself, so i'm quite fuzzy about the details. but there is a PHP function that executes PHP that is stored in a string variable. this is the closest thing i can think of to solve your problem. look around the manual and you'll eventually find a function that executes PHP.

FrozNic

yeah, but then somone could type in some php string that could delete a file or w/e and then ur script is certainly not secure

erikwebb

that's why this function is quite useless. but....you could take the string take out everything except numbers and operators and execute that, maybe.....i honnestly don't understand the purpose you have for doing this.

FrozNic

have u ever used derive 5?

probly not. it's a math program basically.. u put in an equation. it solves it for u. it's basically just a project i came up with. but anyway the point. this is what the program will do (someday lol)
i put in 5x+3=8 (solves for x) that's what the plan is.. so it's going to be much bigger then just a simple 5+5=x because it's going to get much more then just normal values.. hence it will be fun to have as open source because i can't find ANYTHING like this built in php anywhere.

DeltaRho2K

Sure erikwebb, you can script php to perform calculations, but there is no specific function that will calculate a variable where the variable IS a math calculation... You would have to explode the variable into its basics, so your 2+2 gives you the 3 specific variables of 2, the operator, and 2; and then perform your calculation...

Froznic, you already knew this though ;-) I can appreciate your not wanting to do this from scratch, but given that fact, I think you have the skills to write all of the necessary modules to make this happen.

It sounds tough, but sounds like it would be a fun project to develop though...

laserlight

Well, this has been done in other programming languages.

Might be possible to translate those implementations to PHP, if you can get your hands on the source code.

jayant

for solving things like 5+5= ?
is easy

just ask the person to give the input as $result = 5+5

then
just eval it and echo $result

for :-
5x+3=8 (solves for x)

one easy way is to have the person to express it in a valid expression form

=> $result = $expression

=> user gives $result = (8-3)/5;

it gets eval'd as in above case.

for a little bit complex case involving multiple variables we can have it the same way

$var1 = 9;
$var2 = $var1*$var1+$var1+8;
$result = sqrt($var1+$var2);

when this is the input there will be no problem.

but for cases like

8*$var1 = $var2

the above method wont work

for these type of case you will need to make a compiler/interpreter (its pretty easy to make for things like this if you know how to 🙂 )

like to solve a linear equation in 1 variable use can use the general form

ax + b = c
where a,b,c are constant and x is the variable, and let the compiler/interpretor return you values of a,b,c
then u can simple calculate x by (c-b)/a

if you move on to more complex equations, the compiler will also become equally complex.

you might like to look as tools LEX and YACC available in linux which will make a compiler for you in C. convert that to php.

erikwebb

I apologize for lack of a better solution, but parsing the string into arrays of operators and operands is the only way to do this in pure PHP (that I know of). I agree with laserlight, I have seen this sort of things in other programs, but I have never cared enough to look up how it was done. Look for these and you may find a simpler solution that what any of us have thought of.

br__ken

kind of the same thing, i was playing with eval a few months ago, just happened to have it saved: see attachment

Merve

You might be able to do it like this.

<?php
$equation = "5+5";
$explosion = explode ("+",$equation);
$evaluation = $explosion[0]+$explosion[1];
print ("$evaluation");
?>

The only problem with this is that you could only do addition. I don't know if you can put "+ or - or * or / or %" in explode() for the string separator.