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I want to calculate math expression from a string. I have read that the solution to this is to use eval(). But when I try to run the following code:
<?php
$ma ="2+10";
$p = eval($ma);
print $p;
?>
It gives me the following error:
Parse error: syntax error, unexpected $end in
C:\xampp\htdocs\eclipseWorkspaceWebDev\MandatoryHandinSite\tester.php(4)
: eval()'d code on line 1
Does someone know the solution to this problem.
While I don't suggest using eval for this (it is not the solution), the problem is that eval expects complete lines of code, not just fragments.
$ma ="2+10";
$p = eval('return '.$ma.';');
print $p;
Should do what you want.
A better solution would be to write a tokenizer/parser for your math expression. Here's a very simple regex-based one to give you an example:
$ma = "2+10";
if(preg_match('/(\d+)(?:\s*)([\+\-\*\/])(?:\s*)(\d+)/', $ma, $matches) !== FALSE){
$operator = $matches[2];
switch($operator){
case '+':
$p = $matches[1] + $matches[3];
break;
case '-':
$p = $matches[1] - $matches[3];
break;
case '*':
$p = $matches[1] * $matches[3];
break;
case '/':
$p = $matches[1] / $matches[3];
break;
}
echo $p;
}
Take a look at this..
I use this in an accounting system where you can write math expressions in amount input fields..
Examples
$Cal = new Field_calculate();
$result = $Cal->calculate('5+7'); // 12
$result = $Cal->calculate('(5+9)*5'); // 70
$result = $Cal->calculate('(10.2+0.5*(2-0.4))*2+(2.1*4)'); // 30.4
Code
class Field_calculate {
const PATTERN = '/(?:\-?\d+(?:\.?\d+)?[\+\-\*\/])+\-?\d+(?:\.?\d+)?/';
const PARENTHESIS_DEPTH = 10;
public function calculate($input){
if(strpos($input, '+') != null || strpos($input, '-') != null || strpos($input, '/') != null || strpos($input, '*') != null){
// Remove white spaces and invalid math chars
$input = str_replace(',', '.', $input);
$input = preg_replace('[^0-9\.\+\-\*\/\(\)]', '', $input);
// Calculate each of the parenthesis from the top
$i = 0;
while(strpos($input, '(') || strpos($input, ')')){
$input = preg_replace_callback('/\(([^\(\)]+)\)/', 'self::callback', $input);
$i++;
if($i > self::PARENTHESIS_DEPTH){
break;
}
}
// Calculate the result
if(preg_match(self::PATTERN, $input, $match)){
return $this->compute($match[0]);
}
// To handle the special case of expressions surrounded by global parenthesis like "(1+1)"
if(is_numeric($input)){
return $input;
}
return 0;
}
return $input;
}
private function compute($input){
$compute = create_function('', 'return '.$input.';');
return 0 + $compute();
}
private function callback($input){
if(is_numeric($input[1])){
return $input[1];
}
elseif(preg_match(self::PATTERN, $input[1], $match)){
return $this->compute($match[0]);
}
return 0;
}
}
I recently created a PHP package that provides a math_eval helper function. It does exactly what you need, without the need to use the potentially unsafe eval function.
You just pass in the string version of the mathematical expression and it returns the result.
$two = math_eval('1 + 1');
$three = math_eval('5 - 2');
$ten = math_eval('2 * 5');
$four = math_eval('8 / 2');
You can also pass in variables, which will be substituted if needed.
$ten = math_eval('a + b', ['a' => 7, 'b' => 3]);
$fifteen = math_eval('x * y', ['x' => 3, 'y' => 5]);
Link: https://github.com/langleyfoxall/math_eval
Using eval function is very dangerous when you can't control the string argument.
Try Matex for safe Mathematical formulas calculation.
Solved!
<?php
function evalmath($equation)
{
$result = 0;
// sanitize imput
$equation = preg_replace("/[^a-z0-9+\-.*\/()%]/","",$equation);
// convert alphabet to $variabel
$equation = preg_replace("/([a-z])+/i", "\$$0", $equation);
// convert percentages to decimal
$equation = preg_replace("/([+-])([0-9]{1})(%)/","*(1\$1.0\$2)",$equation);
$equation = preg_replace("/([+-])([0-9]+)(%)/","*(1\$1.\$2)",$equation);
$equation = preg_replace("/([0-9]{1})(%)/",".0\$1",$equation);
$equation = preg_replace("/([0-9]+)(%)/",".\$1",$equation);
if ( $equation != "" ){
$result = #eval("return " . $equation . ";" );
}
if ($result == null) {
throw new Exception("Unable to calculate equation");
}
echo $result;
// return $equation;
}
$a = 2;
$b = 3;
$c = 5;
$f1 = "a*b+c";
$f1 = str_replace("a", $a, $f1);
$f1 = str_replace("b", $b, $f1);
$f1 = str_replace("c", $c, $f1);
evalmath($f1);
/*if ( $equation != "" ){
$result = #eval("return " . $equation . ";" );
}
if ($result == null) {
throw new Exception("Unable to calculate equation");
}
echo $result;*/
?>
This method has two major drawbacks:
Security, php script is being evaluated by the eval function. This is bad,
especially when the user wants to inject malicious code.
Complexity
I created this, check it out: Formula Interpreter
How does it work ?
First, create an instance of FormulaInterpreter with the formula and its parameters
$formulaInterpreter = new FormulaInterpreter("x + y", ["x" => 10, "y" => 20]);
Use the execute() method to interpret the formula. It will return the result:
echo $formulaInterpreter->execute();
in a single line
echo (new FormulaInterpreter("x + y", ["x" => 10, "y" => 20]))->execute();
Examples
# Formula: speed = distance / time
$speed = (new FormulaInterpreter("distance/time", ["distance" => 338, "time" => 5]))->execute() ;
echo $speed;
#Venezuela night overtime (ordinary_work_day in hours): (normal_salary * days_in_a_work_month)/ordinary_work_day
$parameters = ["normal_salary" => 21000, "days_in_a_work_month" => 30, "ordinary_work_day" => 8];
$venezuelaLOTTTArt118NightOvertime = (new FormulaInterpreter("(normal_salary/days_in_a_work_month)/ordinary_work_day", $parameters))->execute();
echo $venezuelaLOTTTArt118NightOvertime;
#cicle area
$cicleArea = (new FormulaInterpreter("3.1416*(radio*radio)", ["radio" => 10]))->execute();
echo $cicleArea;
About the formulas
It must contain at least two operands and an operator.
Operands' name could be in upper or lower case.
By now, math functions as sin, cos, pow… are not included. I'm working to include them.
If your formula is not valid, you will get an error message like: Error, your formula (single_variable) is not valid.
Parameters' values must be numeric.
You can improve it if you want to!
eval Evaluates the given code as PHP. Meaning that it will execute the given paremeter as a PHP piece of code.
To correct your code, use this :
$ma ="print (2+10);";
eval($ma);
Using eval function
protected function getStringArthmeticOperation($value, $deduct)
{
if($value > 0){
$operator = '-';
}else{
$operator = '+';
}
$mathStr = '$value $operator $deduct';
eval("\$mathStr = \"$mathStr\";");
$userAvailableUl = eval('return '.$mathStr.';');
return $userAvailableUl;
}
$this->getStringArthmeticOperation(3, 1); //2
Finding a sweetspot between the dangers of eval and the limitless calculation possibilities I suggest checking the input for only numbers, operators and brackets:
if (preg_match('/^[0-9\+\-\*\/\(\)\.]+$/', $mathString)) {
$value = eval('return
' . $mathString . ';');
} else {
throw new \Exception('Invalid calc() value: ' . $mathString);
}
It's still easy to use yet relatively save. And it can handle any basic math calulation like (10*(1+0,2)) which isn't possible with most of the mentioned solutions here.
An eval'd expression should end with ";"
Try this :
$ma ="2+10;";
$p = eval($ma);
print $p;
By the way, this is out of scope but the 'eval' function won't return the value of the expression. eval('2+10') won't return 12.
If you want it to return 12, you should eval('return 2+10;');
I want to calculate math expression from a string. I have read that the solution to this is to use eval(). But when I try to run the following code:
<?php
$ma ="2+10";
$p = eval($ma);
print $p;
?>
It gives me the following error:
Parse error: syntax error, unexpected $end in
C:\xampp\htdocs\eclipseWorkspaceWebDev\MandatoryHandinSite\tester.php(4)
: eval()'d code on line 1
Does someone know the solution to this problem.
While I don't suggest using eval for this (it is not the solution), the problem is that eval expects complete lines of code, not just fragments.
$ma ="2+10";
$p = eval('return '.$ma.';');
print $p;
Should do what you want.
A better solution would be to write a tokenizer/parser for your math expression. Here's a very simple regex-based one to give you an example:
$ma = "2+10";
if(preg_match('/(\d+)(?:\s*)([\+\-\*\/])(?:\s*)(\d+)/', $ma, $matches) !== FALSE){
$operator = $matches[2];
switch($operator){
case '+':
$p = $matches[1] + $matches[3];
break;
case '-':
$p = $matches[1] - $matches[3];
break;
case '*':
$p = $matches[1] * $matches[3];
break;
case '/':
$p = $matches[1] / $matches[3];
break;
}
echo $p;
}
Take a look at this..
I use this in an accounting system where you can write math expressions in amount input fields..
Examples
$Cal = new Field_calculate();
$result = $Cal->calculate('5+7'); // 12
$result = $Cal->calculate('(5+9)*5'); // 70
$result = $Cal->calculate('(10.2+0.5*(2-0.4))*2+(2.1*4)'); // 30.4
Code
class Field_calculate {
const PATTERN = '/(?:\-?\d+(?:\.?\d+)?[\+\-\*\/])+\-?\d+(?:\.?\d+)?/';
const PARENTHESIS_DEPTH = 10;
public function calculate($input){
if(strpos($input, '+') != null || strpos($input, '-') != null || strpos($input, '/') != null || strpos($input, '*') != null){
// Remove white spaces and invalid math chars
$input = str_replace(',', '.', $input);
$input = preg_replace('[^0-9\.\+\-\*\/\(\)]', '', $input);
// Calculate each of the parenthesis from the top
$i = 0;
while(strpos($input, '(') || strpos($input, ')')){
$input = preg_replace_callback('/\(([^\(\)]+)\)/', 'self::callback', $input);
$i++;
if($i > self::PARENTHESIS_DEPTH){
break;
}
}
// Calculate the result
if(preg_match(self::PATTERN, $input, $match)){
return $this->compute($match[0]);
}
// To handle the special case of expressions surrounded by global parenthesis like "(1+1)"
if(is_numeric($input)){
return $input;
}
return 0;
}
return $input;
}
private function compute($input){
$compute = create_function('', 'return '.$input.';');
return 0 + $compute();
}
private function callback($input){
if(is_numeric($input[1])){
return $input[1];
}
elseif(preg_match(self::PATTERN, $input[1], $match)){
return $this->compute($match[0]);
}
return 0;
}
}
I recently created a PHP package that provides a math_eval helper function. It does exactly what you need, without the need to use the potentially unsafe eval function.
You just pass in the string version of the mathematical expression and it returns the result.
$two = math_eval('1 + 1');
$three = math_eval('5 - 2');
$ten = math_eval('2 * 5');
$four = math_eval('8 / 2');
You can also pass in variables, which will be substituted if needed.
$ten = math_eval('a + b', ['a' => 7, 'b' => 3]);
$fifteen = math_eval('x * y', ['x' => 3, 'y' => 5]);
Link: https://github.com/langleyfoxall/math_eval
Using eval function is very dangerous when you can't control the string argument.
Try Matex for safe Mathematical formulas calculation.
Solved!
<?php
function evalmath($equation)
{
$result = 0;
// sanitize imput
$equation = preg_replace("/[^a-z0-9+\-.*\/()%]/","",$equation);
// convert alphabet to $variabel
$equation = preg_replace("/([a-z])+/i", "\$$0", $equation);
// convert percentages to decimal
$equation = preg_replace("/([+-])([0-9]{1})(%)/","*(1\$1.0\$2)",$equation);
$equation = preg_replace("/([+-])([0-9]+)(%)/","*(1\$1.\$2)",$equation);
$equation = preg_replace("/([0-9]{1})(%)/",".0\$1",$equation);
$equation = preg_replace("/([0-9]+)(%)/",".\$1",$equation);
if ( $equation != "" ){
$result = #eval("return " . $equation . ";" );
}
if ($result == null) {
throw new Exception("Unable to calculate equation");
}
echo $result;
// return $equation;
}
$a = 2;
$b = 3;
$c = 5;
$f1 = "a*b+c";
$f1 = str_replace("a", $a, $f1);
$f1 = str_replace("b", $b, $f1);
$f1 = str_replace("c", $c, $f1);
evalmath($f1);
/*if ( $equation != "" ){
$result = #eval("return " . $equation . ";" );
}
if ($result == null) {
throw new Exception("Unable to calculate equation");
}
echo $result;*/
?>
This method has two major drawbacks:
Security, php script is being evaluated by the eval function. This is bad,
especially when the user wants to inject malicious code.
Complexity
I created this, check it out: Formula Interpreter
How does it work ?
First, create an instance of FormulaInterpreter with the formula and its parameters
$formulaInterpreter = new FormulaInterpreter("x + y", ["x" => 10, "y" => 20]);
Use the execute() method to interpret the formula. It will return the result:
echo $formulaInterpreter->execute();
in a single line
echo (new FormulaInterpreter("x + y", ["x" => 10, "y" => 20]))->execute();
Examples
# Formula: speed = distance / time
$speed = (new FormulaInterpreter("distance/time", ["distance" => 338, "time" => 5]))->execute() ;
echo $speed;
#Venezuela night overtime (ordinary_work_day in hours): (normal_salary * days_in_a_work_month)/ordinary_work_day
$parameters = ["normal_salary" => 21000, "days_in_a_work_month" => 30, "ordinary_work_day" => 8];
$venezuelaLOTTTArt118NightOvertime = (new FormulaInterpreter("(normal_salary/days_in_a_work_month)/ordinary_work_day", $parameters))->execute();
echo $venezuelaLOTTTArt118NightOvertime;
#cicle area
$cicleArea = (new FormulaInterpreter("3.1416*(radio*radio)", ["radio" => 10]))->execute();
echo $cicleArea;
About the formulas
It must contain at least two operands and an operator.
Operands' name could be in upper or lower case.
By now, math functions as sin, cos, pow… are not included. I'm working to include them.
If your formula is not valid, you will get an error message like: Error, your formula (single_variable) is not valid.
Parameters' values must be numeric.
You can improve it if you want to!
eval Evaluates the given code as PHP. Meaning that it will execute the given paremeter as a PHP piece of code.
To correct your code, use this :
$ma ="print (2+10);";
eval($ma);
Using eval function
protected function getStringArthmeticOperation($value, $deduct)
{
if($value > 0){
$operator = '-';
}else{
$operator = '+';
}
$mathStr = '$value $operator $deduct';
eval("\$mathStr = \"$mathStr\";");
$userAvailableUl = eval('return '.$mathStr.';');
return $userAvailableUl;
}
$this->getStringArthmeticOperation(3, 1); //2
Finding a sweetspot between the dangers of eval and the limitless calculation possibilities I suggest checking the input for only numbers, operators and brackets:
if (preg_match('/^[0-9\+\-\*\/\(\)\.]+$/', $mathString)) {
$value = eval('return
' . $mathString . ';');
} else {
throw new \Exception('Invalid calc() value: ' . $mathString);
}
It's still easy to use yet relatively save. And it can handle any basic math calulation like (10*(1+0,2)) which isn't possible with most of the mentioned solutions here.
An eval'd expression should end with ";"
Try this :
$ma ="2+10;";
$p = eval($ma);
print $p;
By the way, this is out of scope but the 'eval' function won't return the value of the expression. eval('2+10') won't return 12.
If you want it to return 12, you should eval('return 2+10;');
Is there an elegant way to check if multiple, but not all, conditions are true out of any given number of conditions?
For example, I have three variables: $a, $b, and $c.
I want to check that any two of these are true. So the following would pass:
$a = true;
$b = false;
$c = true;
But this wouldn't:
$a = false;
$b = false;
$c = true;
Also, I may want to check if 4 out of 7 conditions were true, for example.
I realise I can check each combination, but this would get more difficult as the number of conditions increased. Looping through the conditions and keeping a tally is the best option I can think of, but I thought there may be a different way to do this.
Thanks!
Edit: Thanks for all the great answers, they're much appreciated.
Just to throw a spanner in to the works, what if the variables weren't explicit booleans?
E.g.
($a == 2)
($b != "cheese")
($c !== false)
($d instanceof SomeClass)
A "true" boolean in PHP casts to a 1 as an integer, and "false" casts to 0. Hence:
echo $a + $b +$c;
...will output 2 if two out of the three boolean variables $a, $b or $c are true. (Adding the values will implicitly convert them to integers.)
This will also work with functions like array_sum(), so for example:
echo array_sum([true == false, 'cheese' == 'cheese', 5 == 5, 'moon' == 'green cheese']);
...will output 2.
You could put your variables in an array, and use array_filter() and count() to check the number of true values:
$a = true;
$b = false;
$c = true;
if (count(array_filter(array($a, $b, $c))) == 2) {
echo "Success";
};
I'd go for a method like the following:
if (evaluate(a, b, c))
{
do stuff;
}
boolean evaluate(boolean a, boolean b, boolean c)
{
return a ? (b || c) : (b && c);
}
What it says is:
If a is True, then one of b or c must be true too to comply with 2/3
True criterion.
Else, both b and c must be true!
If you want to expand and customise the conditions and the number of variables I'd go for for a solution like the following:
$a = true;
$b = true;
$c = true;
$d = false;
$e = false;
$f = true;
$condition = 4/7;
$bools = array($a, $b, $c, $d, $e, $f);
$eval = count(array_filter($bools)) / sizeof($bools);
print_r($eval / $condition >= 1 ? true : false);
Simply we evaluate the true's and we make sure that the % of True is equals or is better than what we want to achieve. Likewise you could manipulate the final evaluation expression to achieve what you want.
This should also work, and would allow you fairly easily to adjust to the numbers.
$a = array('soap','soap');
$b = array('cake','sponge');
$c = array(true,true);
$d = array(5,5);
$e = false;
$f = array(true,true);
$g = array(false,true);
$pass = 4;
$ar = array($a,$b,$c,$d,$e,$f,$g);
var_dump(trueornot($ar,$pass));
function trueornot($number,$pass = 2){
$store = array();
foreach($number as $test){
if(is_array($test)){
if($test[0] === $test[1]){
$store[] = 1;
}
}else{
if(!empty($test)){
$store[] = 1;
}
}
if(count($store) >= $pass){
return TRUE;
}
}
return false;
}
U can use while loop :
$condition_n = "x number"; // number of required true conditions
$conditions = "x number"; // number of conditions
$loop = "1";
$condition = "0";
while($loop <= $conditions)
{
// check if condition is true
// if condition is true : $condition = $condition + 1;
// $loop = $loop + 1;
}
if($condition >= $condition_n)
{
// conditions is True
}
else
{
// conditions is false
}
I think it is a little easy and short writing when you use operator "&" , "|" like this:
$a = true;
$b = true;
$c = false;
$isTrue = $a&$b | $b&$c | $c&$a;
print_r( $isTrue );
Let check by your self :D
I'm curious if it's possible to string along a couple possibilities for a function in an if statement, link them to a single variable and return the one that works, if any.
The following doesn't work, but it demonstrates the idea. I'd like the below to return 2 since the function myFn() only returns true when 2 is passed to it.
But instead the following returns true: 1.
if ($b = myFn(1) || $b = myFn(2) || $b = myFn(3)) {
echo 'true: ' . $b;
} else {
echo 'false: ' . $b;
}
function myFn($a) {
if ($a == 2) return $a;
return false;
}
Short of adding a series of elseifs, is there a way to string the functions in a series of ORs while only returning the successful one?
codepad: http://codepad.org/ldiCxY4j
Just wrap each assignment in parenthesis:
(($b = myFn(1)) || ($b = myFn(2)) || ($b = myFn(3)))
See: PHP operator precedence
When using logical operators, PHP coerces the result to boolean. Without the extra parens, it echoes '1' because echoing coerces true to '1'.
You may be better off using a loop:
/**
* Get the first $array value that passes the $test, or else null.
* #return mixed|null
*/
function find ($array, $test) {
foreach ($array as $index => $value) {
if (call_user_func($test, $value, $index, $array))
return $value;
}
}
For such concatenations of assignments PHP has the or operator, which is the same as || but with less precedence than =. This means that
if ($b = myFn(1) or $b = myFn(2) or $b = myFn(3))
is treated like:
if (($b = myFn(1)) or ($b = myFn(2)) or ($b = myFn(3)))
while
if ($b = myFn(1) || $b = myFn(2) || $b = myFn(3))
is treated like:
if ($b = (myFn(1) || $b = (myFn(2) || $b = myFn(3))))
If I have a php string called $a. It can either end in a k or not end with a k.
If it ends with a k, then I want to do nothing, but if it does not end with a k then I want to add the string $b to the end. How can I recognise what the string $a ends with to do this?
$a=asdk ----> do nothing
$a=asdtt ---->add string $b(=rrk say) to make it $a=asdttrrk
Use this method:
if ($a[strlen($a) -1] !== 'k') $a .= $b;
alternative
if (substr($a, -1) !== 'k') $a .= $b;
You can access a specific character using $a[i], so the last character would be $a[strlen($a) - 1].
$last_char = $a[count($a) - 1];
if ($last_char == 'k') {
//do stuff here
}
There is also substr_compare:
// test 1
$a = "asdfasdf";
$b = "foo";
$a .= (substr_compare($a, 'k', -strlen('k'), strlen('k')) === 0) ? "" : $b;
echo $a; // asdfasdffoo
echo "\n\n";
// test 2
$a = "asdfasdkkkk";
$b = "foo";
$a .= (substr_compare($a, 'k', -strlen('k'), strlen('k')) === 0) ? "" : $b;
echo $a; // asdfasdkkkk
Try it out here.
function isLast($str) {
return $str[strlen($str)-1];
}
$string = 'abcdefghijk';
if(isLast($string) == 'k') {
echo 'true';
}
else {
echo 'false';
}
Yet another version (if you prefer using custom functions)