For example I have a statement:
$var = '2*2-3+8'; //variable type is string
How to make it to be equal 9 ?
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1Care to pay attention to the "Related" section of the page? A duplocate of how to evaluate formula passed as string in php?Your Common Sense– Your Common Sense2011-11-17 08:41:56 +00:00Commented Nov 17, 2011 at 8:41
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ok, sorry I found also this: stackoverflow.com/questions/5057320/…rsk82– rsk822011-11-17 08:54:10 +00:00Commented Nov 17, 2011 at 8:54
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4 Answers
From this page, a very awesome (simple) calculation validation regular expression, written by Richard van Velzen. Once you have that, and it matches, you can rest assured that you can use eval over the string. Always make sure the input is validated before using eval!
<?php
$regex = '{
\A # the absolute beginning of the string
\h* # optional horizontal whitespace
( # start of group 1 (this is called recursively)
(?:
\( # literal (
\h*
[-+]? # optionally prefixed by + or -
\h*
# A number
(?: \d* \. \d+ | \d+ \. \d* | \d+) (?: [eE] [+-]? \d+ )?
(?:
\h*
[-+*/] # an operator
\h*
(?1) # recursive call to the first pattern.
)?
\h*
\) # closing )
| # or: just one number
\h*
[-+]?
\h*
(?: \d* \. \d+ | \d+ \. \d* | \d+) (?: [eE] [+-]? \d+ )?
)
# and the rest, of course.
(?:
\h*
[-+*/]
\h*
(?1)
)?
)
\h*
\z # the absolute ending of the string.
}x';
$var = '2*2-3+8';
if( 0 !== preg_match( $regex, $var ) ) {
$answer = eval( 'return ' . $var . ';' );
echo $answer;
}
else {
echo "Invalid calculation.";
}
Comments
What you have to do is find or write a parser function that can properly read equations and actually calculate the outcome. In a lot of languages this can be implemented by use of a Stack, you should have to look at things like postfix and infix parsers and the like.
Hope this helps.
2 Comments
Your Common Sense
not to mention that there are tons of ready-made parsers right here in stackoverflow answers
SegF4ult
Col. Shrapnel is probably right, I didn't have the time to look for ready-made parsers, good luck!
$string_with_expression = '2+2';
eval('$eval_result = ' . $string_with_expression)`;
$eval_result - is what you need.
