PHP practice function ($result) can't be called

Solution:

I think you are confused by the short open tag

if I print

<?=$result;?>
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or

<?=cal_result($first_num,$second_num,$operator);?>
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this is the same thing like

<?php echo $result;?>
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or

<?php echo cal_result($first_num,$second_num,$operator);?>
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If you call a function that ВґreturnsВґ values, and you want to use them , you must also print them out...

also check out global variables. If you want to use $result outside the function scope you must declare it a global variable.

<?php
  $result = '';
  $first_num = 0;
  $second_num = 0;
  
  $ops = array( "+", 
                "-",
                "Г—",  // HTML : &times; , ASCII CODE : 158 
                "Г·"); //  HTML : &divide; , ASCII CODE : 246

  // checking if the first number is what he should be
  if ( isset($_POST['first_num']) && 
      !empty($_POST['first_num']) && 
      is_numeric($_POST['first_num']) )
  {
    $first_num = $_POST['first_num'];
  }

  // checking if the second number is what he should be
  if ( isset($_POST['second_num']) && 
      !empty($_POST['second_num']) && 
      is_numeric($_POST['second_num']) )
  {
    $second_num = $_POST['first_num'];
  }
  
  function cal_result($first_num,$second_num,$operator){
    
    // optionally you can assign global
    global $result;
    
    // here we prevent injection by acceptint only operators from the ops array
    if (isset($_GET['operator']) && in_array($_GET['operator'],$ops)) {
      switch ($_GET['operator']) {
        case $ops[0]: // first element of array ops is Add
          $result = $first_num + $second_num;
          // remember this function is just returning the $result 
          // variable it is not printing it, you will have to assiging 
          // the function to a variable if you want to use the  
          return $result;
        break;
        case $ops[1]: // second element of array ops is Subtract
          $result = $first_num - $second_num;
          return $result;
        break;
        case $ops[2]: // third element of array ops is Multiply
          $result = $first_num * $second_num;
          return $result;
        break;
        case $ops[3]: // fourth element of array ops is Divide
          // divide by zero problem
          if($second_num !== 0){
            $result = $first_num / $second_num;
          }else{
            $result = "Err: Div By Zero";
          }
          return $result;
        break;
      }
    }    
  }
}



?>
<p>
    <!--// now you have 2 possibilities :                 //-->
    <!--// first you can call the global variable $result //-->
    <label for="quiz-form"><?=$result;?></label>

    <!--// the second possibility is to call the function //-->
    <label for="quiz-form"><?=cal_result($first_num,$second_num,$operator);?></label>

    <b>Result</b>
</p>
<!-- for post you should also set enctype for security reasons -->
<form action="simple_calculator.php" 
      method="post" 
      id="quiz-form" 
      enctype="application/x-www-form-urlencoded">
        <p>
            <input  type="number" 
                    name="first_num" 
                    id="first_num" 
                    required="required" 
                    value="<?=$first_num;?>" />
            <b>First Number</b>
        </p>
        <p>
            <input  type="number" 
                    name="second_num" 
                    id="second_num" 
                    required="required" 
                    value="<?=$second_num;?>" />
            <b>Second Number</b>
        </p>
        <input type="submit" name="operator" value="+" alt="Add" />
        <input type="submit" name="operator" value="-" alt="Subtract" />
        <input type="submit" name="operator" value="Г—" alt="Multiply" />
        <input type="submit" name="operator" value="Г·" alt="Divide" />
</form>
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