<!-- ================== calculator.php : below ================== -->
<?php
$first_num = null;
$second_num = null;
$operator = null;
$result = null;
//===== TODO: write your code below =====
//===== TODO: write your code above =====
?>
<!doctype html>
<html lang="en">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="//stackpath.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" integrity="sha384-WskhaSGFgHYWDcbwN70/dfYBj47jz9qbsMId/iRN3ewGhXQFZCSftd1LZCfmhktB" crossorigin="anonymous">
<title>PHP Calculator</title>
</head>
<body>
<div class="container">
<form action="calculator.php" method="post">
<div class="form-row">
<div class="form-group col-md-2">
<input type="number" class="form-control" id="first_num" name="first_num" value="<?php echo $first_num; ?>">
</div>
<div class="form-group col-md-1">
<select class="form-control" id="operator" name="operator">
<option <?php if($operator == 0){ echo "selected"; } ?> value="0">+</option>
<option <?php if($operator == 1){ echo "selected"; } ?> value="1">-</option>
<option <?php if($operator == 2){ echo "selected"; } ?> value="2">✕</option>
<option <?php if($operator == 3){ echo "selected"; } ?> value="3">÷</option>
</select>
</div>
<div class="form-group col-md-2">
<input type="number" class="form-control" id="second_num" name="second_num" value="<?php echo $second_num; ?>">
</div>
<label class="col-md-1 col-form-label">=</label>
<label class="col-md-1 col-form-label"><?php echo $result; ?></label>
</div>
<button type="submit" class="btn btn-primary">Calculate</button>
</form>
</div>
</body>
</html>
<!-- ================== calculator.php : abobe ================== -->
This calculator has functions of addition, subtraction, multiplication and division.
When the Calculate button is pressed, the screen transitions and the input value and calculation result are displayed.
ex)
- Write your code inside the "TODO" comment in calculator.php.