<form method="post" action="">
			<input type="hidden" name="x" id="hiddenX" value="500">
			<input type="hidden" name="y" id="hiddenY" value="699">
			<input type="hidden" name="age" id="hiddenAge" value="">		
    <button type="submit" name="submit">Calculate</button>
</form>


<?php
    if ($_SERVER['REQUEST_METHOD'] == 'POST') {
        $x = $_POST['x'];
        $y = $_POST['y'];
        $age = $_POST['age'];

        $xx = number_format($x);
        $yy = ($y * 1);
        $yy1 = ($y * 3);
        $yy3 = ($y * 2);
        $yy6 = ($y * 4);
        
        echo "<p>Selected age: $age</p>";

        $initial_yy_value = 1000;
        $initial_yy1_value = 1000;
        $initial_value = 1000;
        $xx_increase_per_year = $xx;

        $yy_increase_per_year = $yy;
        $yy1_increase_per_year = $yy1;

        // Set up data arrays
        $labels = [];
        $xx_data = [];
        $yy_data = [];
        $yy1_data = [];

        // Generate data for chart
        $current_age = $age;
        $max_age = min($age + 20, 100);
        while ($current_age <= $max_age) {
            $labels[] = $current_age;

            $xx_data[] = $initial_value;
            $initial_value += $xx_increase_per_year;

            $yy_data[] = $current_age <= 65 ? $yy_increase_per_year : 0;

            $initial_yy1_value += $yy1_increase_per_year;
            $yy1_data[] = $initial_yy1_value;

            $current_age++;
        }

        // Set up data object for chart.js
        $data = [
            'labels' => $labels,
            'datasets' => [
                [
                    'label' => '$xx',
                    'data' => $xx_data,
                    'backgroundColor' => 'rgba(255, 99, 132, 0.2)',
                    'borderColor' => 'rgba(255, 99, 132, 1)',
                    'borderWidth' => 1
                ],
                [
                    'label' => '$yy',
                    'data' => $yy_data,
                    'backgroundColor' => 'rgba(54, 162, 235, 0.2)',
                    'borderColor' => 'rgba(54, 162, 235, 1)',
                    'borderWidth' => 1
                ],
                [
                    'label' => '$yy1',
                    'data' => $yy1_data,
                    'backgroundColor' => 'rgba(255, 206, 86, 0.2)',
                    'borderColor' => 'rgba(255, 206, 86, 1)',
                    'borderWidth' => 1
                ]
            ]
        ];
        $data_json = json_encode($data);
    }
?>


   <script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
    <canvas id="myChart"></canvas>
    <script>
        var ctx = document.getElementById('myChart').getContext('2d');
        var chart = new Chart(ctx, {
            type: 'line',
            data: <?php echo $data_json; ?>,
            options: {}
        });
    </script>

แบบ ใส่ค่าก่อน

<form method="post" action="">
    <input type="text" name="x" id="inputX" value="">
    <input type="text" name="y" id="inputY" value="">
    <input type="text" name="age" id="inputAge" value="">	
    <button type="submit" name="submit">Calculate</button>
</form>


<?php
    if ($_SERVER['REQUEST_METHOD'] == 'POST') {
        $x = $_POST['x'];
        $y = $_POST['y'];
        $age = $_POST['age'];

        $xx = number_format($x);
        $yy = ($y * 1);
        $yy1 = ($y * 3);
        $yy3 = ($y * 2);
        $yy6 = ($y * 4);
        
        echo "<p>Selected age: $age</p>";

        $initial_yy_value = 1000;
        $initial_yy1_value = 1000;
        $initial_value = 1000;
        $xx_increase_per_year = $xx;

        $yy_increase_per_year = $yy;
        $yy1_increase_per_year = $yy1;

        // Set up data arrays
        $labels = [];
        $xx_data = [];
        $yy_data = [];
        $yy1_data = [];

        // Generate data for chart
        $current_age = $age;
        $max_age = min($age + 20, 100);
        while ($current_age <= $max_age) {
            $labels[] = $current_age;

            $xx_data[] = $initial_value;
            $initial_value += $xx_increase_per_year;

            $yy_data[] = $current_age <= 65 ? $yy_increase_per_year : 0;

            $initial_yy1_value += $yy1_increase_per_year;
            $yy1_data[] = $initial_yy1_value;

            $current_age++;
        }

        // Set up data object for chart.js
        $data = [
            'labels' => $labels,
            'datasets' => [
                [
                    'label' => '$xx',
                    'data' => $xx_data,
                    'backgroundColor' => 'rgba(255, 99, 132, 0.2)',
                    'borderColor' => 'rgba(255, 99, 132, 1)',
                    'borderWidth' => 1
                ],
                [
                    'label' => '$yy',
                    'data' => $yy_data,
                    'backgroundColor' => 'rgba(54, 162, 235, 0.2)',
                    'borderColor' => 'rgba(54, 162, 235, 1)',
                    'borderWidth' => 1
                ],
                [
                    'label' => '$yy1',
                    'data' => $yy1_data,
                    'backgroundColor' => 'rgba(255, 206, 86, 0.2)',
                    'borderColor' => 'rgba(255, 206, 86, 1)',
                    'borderWidth' => 1
                ]
            ]
        ];
        $data_json = json_encode($data);
    }
?>


   <script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
    <canvas id="myChart"></canvas>
    <script>
        var ctx = document.getElementById('myChart').getContext('2d');
        var chart = new Chart(ctx, {
            type: 'line',
            data: <?php echo $data_json; ?>,
            options: {}
        });
    </script>