Questions about getting variables in php

PHPcode @ $ judge =$ _ GET [& quot; speed & quot;]; if (@ $ keyboard =$ _ GET [& quot; keyboard & quot;]) {$ keyboardfinal = 100;} if (@ $ judge = 1) {if ($ keyboard about getting variables in php

PHP code

  @$judge=$_GET["speed"];if(@$keyboard=$_GET["keyboard"]){$keyboardfinal=100;}if(@$judge==1){if($keyboard<40 && $keyboard>0){@$keyboardfinal=50;    }}if(@$judge==2){if(@$keyboard<50&& $keyboard>0){$keyboardfinal=50;    }}if(@$judge==3 && (@$keyboard<170 && @$keyboard>0)){$keyboardfinal=50;    }

Code above ~ In the second, third, and fourth if statements, $ keyboardfinal = 50 cannot be made even if the conditions are true. why?


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@ $ Judge = $ _ GET ["speed"];
Why is the special effect of adding @ in front of the variable?
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I don't understand why I need to add so many error controllers. If no error is reported, how can I modify the code?
Modify the landlord's code:

PHP code

$ Judge = 1; $ keyboard = 35; $ keyboardfinal = null; switch ($ judge) {case 1: if ($ keyboard <40 & $ keyboard> 0) $ keyboardfinal = 50; break; case 2: if ($ keyboard <50 & $ keyboard> 0) $ keyboardfinal = 50; break; case 3 & ($ keyboard <170 & $ keyboard> 0): $ keyboardfinal = 50; break;} echo "keyboardfinal --> ". $ keyboardfinal; #50
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   Discussion
   
PHP code
   
@ $ Judge = $ _ GET ["speed"];
   
If (@ $ keyboard = $ _ GET ["keyboard"]) {
   
$ Keyboardfinal = 100;
   
}
   
If (@ $ judge = 1 ){
   
If ($ keyboard <40 & $ keyboard> 0 ){
   
@ $ Keyboardfinal = 50;
   
}
   
}
   
If (@ $ judge = 2 ){
   
If (@ $ keyb ......