I am trying to avoid duplicating my code by checking the variable if it is a certain operator.
Basically..
$op = $_POST['operator'];
$x = 5;
$y = 2;
$result = $x /* $op instead of '+'/'-'/'*'/'/'/'%' */ $y;
Is this possible or will I have to send the operator as a String and duplicate the code per operator type?
It's a lot safer to do something like this:
$x = 5;
$y = 2;
switch($_POST['operator']){
case '+':
$result = $x + $y;
break;
case '-':
$result = $x - $y;
break;
case '*':
$result = $x*$y;
break;
case '/':
$result = $x/$y;
break;
case '%':
$result = $x % $y;
break;
default:
$result = 'Operator not supported';
}
Something along those lines.
Ahem. You can eval.
$result = eval("$x $op $y");
But this is DANGEROUS and you should sanitize your variables with great care. There is a saying that goes something like "If your problem requires use of eval, then the problem is wrong." Something like that. It's almost certainly preferable to do something like this:
function apply_op($x, $y, $op) {
switch ($op) {
case '+': return $x + $y;
...
}
}
you can make this:
$operators = array("+", "-","*","%","/");
$op = $_POST["operator"];
if(in_array($op, $operators)) {
echo eval("$x $op $y");
} else {
echo "Operator not supported";
}
Related
Hy,
I got switch case inside function when but when i call it, i got error Undefined Variable and i don't know why (i use PHP 8)
private function getIDFromBrand() {
switch ($this->brand) {
case "Niky":
$id = 1;
break;
case "Pumo":
$id = 4;
break;
case "Coke":
if ($this->typecoke== 0) {
$id = 2;
} else {
if ($this->typecoke== 1) {
$id = 3;
}
}
break;
case "Tomato":
$id = 5;
break;
case "Riles":
$id = 6;
break;
case "TEST":
$id = 7;
break;
}
return $id; // Error Undefined variable $id
}
When i declare $id at the top of my function, like
$id = null
or
$id = 0
The switch doesn't update it, so it will return null or 0, it will return the declared value.
Your switch statement has no default branch, so if $this->brand is, say, "Stack Overflow", it will not run any of the statements, and $id will never be set.
See the PHP manual for the switch statement:
A special case is the default case. This case matches anything that wasn't matched by the other cases.
Similarly, if $this->brand is "Coke", but $this->typecoke is, say, 42, it will not match either of the conditions in that branch.
switch ($this->brand) {
case "Niky":
$id = 1;
break;
case "Pumo":
$id = 4;
break;
case "Coke":
if ($this->typecoke== 0) {
$id = 2;
} elseif ($this->typecoke== 1) {
$id = 3;
} else {
$id = -1; // WAS PREVIOUSLY NOT SET
}
break;
case "Tomato":
$id = 5;
break;
case "Riles":
$id = 6;
break;
case "TEST":
$id = 7;
break;
default:
$id = -1; // WAS PREVIOUSLY NOT SET
break;
}
if (isset($_POST["submit"])){
$oride='';
$count = "25";
$origin = $_POST["origin"];
$destinataion = $_POST["destination"];
$oride = ($destination = $_POST["destination"] - $origin= $_POST["origin"]);
switch (true) {
case ($count<="0"):
echo "invalid";
break;
case ($count==="15"):
echo $count;
break;
case ($count==="16"):
$total = $count + "1";
echo $total;
break;
default:
echo "hello";
} }
The code will compute 1st then execute switch depending on what is the result of the computation. I tried if else but it will be too long because the case will go up to 130.
You must use the var $count in switch statement and the constant in case this way
switch ($count) {
case "0" :
echo "invalid";
break;
case "15":
echo $count;
break;
case "16":
$total = $count + "1";
echo $total;
break;
default:
echo "hello";
break;
}
You have to provide an expression to the switch statement, while the case statements are just "versions" of the result of that expression. The only thing you can NOT do directly is the "<= 0" expression, but you can work around it:
if (isset($_POST["submit"])){
$oride='';
$count = "25";
$origin = $_POST["origin"];
$destinataion = $_POST["destination"];
$oride = ($destination = $_POST["destination"] - $origin= $_POST["origin"]);
// --- normalize $count:
$count = $count <= 0 ? 0 : $count;
// use $count as expression:
switch ($count) {
case 0:
echo "invalid";
break;
case "15":
echo $count;
break;
case "16":
$total = $count + "1";
echo $total;
break;
default:
echo "hello";
} }
I'm parsing some text and calculating the weight based on some rules. All the characters have the same weight. This would make the switch statement really long can I use ranges in the case statement.
I saw one of the answers advocating associative arrays.
$weights = array(
[a-z][A-Z] => 10,
[0-9] => 100,
['+','-','/','*'] => 250
);
//there are more rules which have been left out for the sake of clarity and brevity
$total_weight = 0;
foreach ($text as $character)
{
$total_weight += $weight[$character];
}
echo $weight;
What is the best way to achieve something like this?
Is there something similar to the bash case statement in php?
Surely writing down each individual character in either the associative array or the switch statement can't be the most elegant solution or is it the only alternative?
Well, you can have ranges in switch statement like:
//just an example, though
$t = "2000";
switch (true) {
case ($t < "1000"):
alert("t is less than 1000");
break
case ($t < "1801"):
alert("t is less than 1801");
break
default:
alert("t is greater than 1800")
}
//OR
switch(true) {
case in_array($t, range(0,20)): //the range from range of 0-20
echo "1";
break;
case in_array($t, range(21,40)): //range of 21-40
echo "2";
break;
}
$str = 'This is a test 123 + 3';
$patterns = array (
'/[a-zA-Z]/' => 10,
'/[0-9]/' => 100,
'/[\+\-\/\*]/' => 250
);
$weight_total = 0;
foreach ($patterns as $pattern => $weight)
{
$weight_total += $weight * preg_match_all ($pattern, $str, $match);;
}
echo $weight_total;
*UPDATE: with default value *
foreach ($patterns as $pattern => $weight)
{
$match_found = preg_match_all ($pattern, $str, $match);
if ($match_found)
{
$weight_total += $weight * $match_found;
}
else
{
$weight_total += 5; // weight by default
}
}
You can specify the character range using regular expression. This saves from writing a really long switch case list. For example,
function find_weight($ch, $arr) {
foreach ($arr as $pat => $weight) {
if (preg_match($pat, $ch)) {
return $weight;
}
}
return 0;
}
$weights = array(
'/[a-zA-Z]/' => 10,
'/[0-9]/' => 100,
'/[+\\-\\/*]/' => 250
);
//there are more rules which have been left out for the sake of clarity and brevity
$total_weight = 0;
$text = 'a1-';
foreach (str_split($text) as $character)
{
$total_weight += find_weight($character, $weights);
}
echo $total_weight; //360
Much different ways to do this.
$var = 0;
$range_const = range(10,20);
switch ($var) {
case 1: $do = 5; break; # 1
case 2: $do = 10; break; # 2
case 3:
case 4:
case 5: $do = 15; break; # 3, 4, 5
default:
if ($var > 5 && $var < 10) { # High performance (6..9)
$do = 20;
} else if (in_array($var, $range_const, true)) { # Looks clear (10..20)
$do = 25;
} else { # NOT in range 1..20
$do = -1;
}
}
print($do);
There no direct range X..Y compares because $var checks to true in each step, but this allows do some nice cheating like this...
$in = create_function('$a,$l,$h', 'return $a>=$l && $a<=$h;');
$var = 4;
switch (true) {
case ($var === 1): echo 1; break;
case ($var === 2): echo 2; break;
case $in($var, 3, 5): echo "3..5"; break;
case $in($var, 6, 10): echo "6..10"; break;
default: echo "else";
}
If you have a more complex conditions, you can wrap them inside a function. Here's an oversimplified example:
$chartID = 20;
$somethingElse = true;
switch (switchRanges($chartID, $somethingElse)) {
case "do this":
echo "This is done";
break;
case "do that":
echo "that is done";
break;
default:
echo "do something different";
}
function switchRanges($chartID, $somethingElse = false)
{
if (in_array($chartID, [20, 30]) && $somethingElse === true) {
return "do this";
}
if (in_array($chartID, [20, 50]) && $somethingElse === false) {
return "do that";
}
}
I think I would do it in a simple way.
switch($t = 100){
case ($t > 99 && $t < 101):
doSomething();
break;
}
How can I solve this problem:
if ($variable == 1) {
$math = "-";
} else {
$math = "+";
}
$numberOne = 10;
$numberTwo = 10;
$result = $numberOne $math $numberTwo;
This doesn´t work, is there any way to solve this?
This will work for your example. A subtraction is the same as adding a negative. This will be far safer than the alternative of using eval.
if ($variable == 1) {
$modifier = -1;
} else {
$modifier = 1;
}
$numberOne = 10;
$numberTwo = 10;
$result = $numberOne + ($numberTwo * $modifier);
I suppose you could use eval() -- but that would be quite a bad idea (it would not be good for performances, it's not "clean", ...)
In this kind of situation, I would generally go with a switch on the operator, and one case per possible operator.
Here, it would mean using something like this :
switch ($math) {
case '+':
$result = $numberOne + $numberTwo;
break;
case '-':
$result = $numberOne - $numberTwo;
break;
}
Which can easily be extends to other operators.
(In your specific situation, if you only have + and -, though, some calculation based on a multiplication by +1 or -1 would be faster to write)
if ($variable == 1) {
$math = -1; // subtraction
} else {
$math = 1; // addition
}
$numberOne = 10;
$numberTwo = 10;
$result = $numberOne + ($math * $numberTwo);
No love for the ternary operator?
To minify Gazler's answer a bit further:
$modifier = ($variable == 1) : -1 ? 1;
$numberOne = 10;
$numberTwo = 10;
$result = $numberOne + ($numberTwo*$modifier);
If you plan to use more complex mathematics, you can use the eval() function.
I wrote this:
$num1 = mt_rand(1,5);
$num2 = mt_rand(1,5);
$operators = array(
"+",
"-",
"*",
"/"
);
$result = $num1 . $operators[array_rand($operators)] . $num2;
(My best guess is) This doesn't work as I expected because in the array the operator is a string which makes everything a string:
var_dump($result);
Gives:
string(3) "4+3"
So my question would be how would you recommend approaching this* without changing the logic it too much?
Thanks in advance!!
*Making random operation among random numbers, and if possible, the operators should be stored in an array.
I have the feeling my title is not correctly describing the situation but I could not come up with a better idea, I'm open to suggestions :)
Of course, you could use eval to do this, but I certainly won't settle for such a solution.
I'd suggest defining a bunch of functions that take in two params and return a result, then use call_user_func_array on the result of array_rand.
function add($x, $y) { return $x + $y; }
function subtract($x, $y) { return $x - $y; }
function multiply($x, $y) { return $x * $y; }
function divide($x, $y) { return $x / $y; }
$operators = array('add', 'subtract', 'multiply', 'divide');
//...
$result = call_user_func_array($operators[array_rand($operators)], array($x, $y));
<?php
$num1 = mt_rand(1, 5);
$num2 = mt_rand(1, 5);
$operators = array(
"+",
"-",
"*",
"/"
);
switch ($operators[array_rand($operators)]) {
case "+":
$result = $num1 + $num2;
break;
case "-":
$result = $num1 - $num2;
break;
case "*":
$result = $num1 * $num2;
break;
case "/":
$result = $num1 / $num2;
break;
}
var_dump($result);
The clean solution would be to have a code branch for each operator, e.g.
function do_something($num1, $num2, $operator) {
switch ($operator) {
case '+':
return $num1 + $num2;
case '-':
return $num1 - $num2;
case '*':
return $num1 * $num2;
case '/':
return $num1 / $num2;
default:
throw new Exception('Unknown operator: '.$operator)
}
}
If you have more operators, you should create a map of operator => function and dynamically call the functions, for example:
$ftable = array(
'+' => 'fn_add',
'-' => 'fn_sub',
'*' => 'fn_mul',
'/' => 'fn_div'
);
function fn_add($a, $b) { return $a + $b; }
function fn_sub($a, $b) { return $a - $b; }
function fn_mul($a, $b) { return $a * $b; }
function fn_div($a, $b) { return $a / $b; }
function do_something($num1, $num2, $operator) {
global $ftable;
if (array_key_exists($operator, $ftable)) {
return call_user_func($ftable[$operator], $num1, $num2);
}
else {
throw new Exception('Unknown operator: '.$operator)
}
}
And of course, the unclean (slow, potentially dangerous) solution would be to use eval().
Create a function for each operation, then store operator => function name in an array.