PHP calculator with one input field

Question

I need to have a text input field do or not do basic calculations. Example

<input type="text" />

I then submit by post and the post will know to either enter the value or do calculations

Value examples

14.5
10.3+14+35

Should give me respectively

14.5
59.3

Does anyone know of a method, script,...anything to do this? Or any idea on how to go about it?

Thanks.

There's always eval()... I don't dare post it as an answer - I'm sure it will invite flames. — No Results Found
– No Results Found, Commented Jun 14, 2011 at 6:34

zaf · Accepted Answer · 2011-06-14 06:58:54Z

4

Without using eval but you still need to be careful and catch any parsing errors, for example trying to evaluate ')' etc. I have ideas but will leave them for the reader or another rainy day.

reference site

function calculate_string( $mathString ) {

    // trim white spaces
    $mathString = trim($mathString);

    // remove any non-numbers chars; exception for math operators
    $mathString = ereg_replace ('[^0-9\+-\*\/\(\) ]', '', $mathString);

    $compute = create_function("", "return (" . $mathString . ");" );
    return 0 + $compute();

}

$string = " (1 + 1) * (2 + 2)";
echo calculate_string($string);  // outputs 8

edited Jun 14, 2011 at 6:58

answered Jun 14, 2011 at 6:44

zaf

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9 Comments

Tom Over a year ago

@Wesley: "open to errors" is not the same as "security hole". @zaf's answer is a solution to the question... the question didn't ask about guaranteeing a valid syntax tree.

zaf Over a year ago

@Tom Thanks Tom - I was about to spend the rest of the day to make it bullet proof...

No Results Found Over a year ago

@Tom: Even though the question didn't ask, we really should be poitning this stuff out when giving advice, as zaf has considerately chosen to do. Aside, I feel like there really must be a legit way to do this.

zaf Over a year ago

@Wesley Munch Maybe you/i should open a question specifically for this itch... I have some crazy ideas...

Tom Over a year ago

@Wesley: what would constitute a correct solution for you? If there's a syntax error in the input calculation, this answer gives an error, which could be directed back to the user using an exception handler. What else should a 'PHP calculator' do?

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Andi Novak · Accepted Answer · 2013-02-07 18:03:22Z

0

With the following regular expression you can check whether the input is valid mathematical syntax and use eval():

/^(\(*[\+\-]?\(*[\+\-]?\d+(.\d+)?\)*[\+\-\*\/]?)*$/

Allowed characters are: 1 2 3 4 5 6 7 8 9 0 . + - * / ( )

edited Feb 7, 2013 at 18:03

answered Feb 7, 2013 at 4:12

Andi Novak

11 bronze badge

Comments

deltaforce2 · Accepted Answer · 2011-06-14 06:37:33Z

-1

One quick solution would be to check with substr() if the input has any math operators (+, -, ...) in it. If so, do the math either using eval() (quite a dirty hack, since it accepts all PHP code and not only math) or build the appropriate tree of operations manually and then produce the results. If there are no math operators, just print out the input.

answered Jun 14, 2011 at 6:37

deltaforce2

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