PHP Top Exercises

Write a factorial program using for loop in php

Description: Write a PHP program to calculate the factorial of a number using a for loop.

Rules and hints:

• Factorial of 5 is 5 x 4 x 3 x 2 x 1 = 120.
• Use a loop that multiplies the numbers one by one.

PHP program for factorial using a for loop

<?php
$num = 5;
$factorial = 1;

for ($x = $num; $x >= 1; $x--) {
    $factorial = $factorial * $x;
}

echo "The factorial of " . $num . " is " . $factorial;
?>

Output:

How it works

• $factorial starts with 1.
• The loop goes from 5 down to 1, and multiplies $factorial with each number.
• The factorial of 0 is 1, and this program gives 1 for it too, because the loop does not run.

Another way is to use a function that calls itself: factorial using recursion.

Write a program to create Chess board in PHP using for loop

Description: Write a PHP program that creates a chess board using nested for loops.

Rules and hints:

• Use an HTML table. Make each square 50px wide and 50px high.
• The squares must be black and white, one after the other.
• Hint: if the sum of the row number and the column number is even, use white, otherwise black.

PHP program to create a chess board

<?php
echo '<table border="1" cellspacing="0" cellpadding="0">';

for ($row = 1; $row <= 8; $row++) {
    echo "<tr>";

    for ($col = 1; $col <= 8; $col++) {
        $color = (($row + $col) % 2 == 0) ? "white" : "black";
        echo '<td style="width:50px;height:50px;background:' . $color . '"></td>';
    }

    echo "</tr>";
}

echo "</table>";
?>

Output:

How it works

• The outer loop creates the 8 rows (<tr>), and the inner loop creates 8 cells (<td>) in every row.
• ($row + $col) % 2 is 0 for every second square, so the colors change like on a real chess board.
• The ternary operator picks the color. See PHP Ternary Operator.

Write a program to calculate Electricity bill in PHP

Description: Write a PHP program to calculate the electricity bill using conditional statements.

Rules and hints:

• Calculate the bill for the units that fall in each slab.
• Write the logic in a function that gets the units and returns the bill.
• Show the amount with 2 decimal digits.

PHP program to calculate the electricity bill

<?php
function electricityBill($units) {
    $bill = 0;

    if ($units > 250) {
        $bill += ($units - 250) * 6.50;
        $units = 250;
    }
    if ($units > 150) {
        $bill += ($units - 150) * 5.20;
        $units = 150;
    }
    if ($units > 50) {
        $bill += ($units - 50) * 4.00;
        $units = 50;
    }
    $bill += $units * 3.50;

    return $bill;
}

echo "Bill for 320 units: Rs. " . number_format(electricityBill(320), 2) . "<br>";
echo "Bill for 120 units: Rs. " . number_format(electricityBill(120), 2);
?>

Output:

How it works

• The function starts from the highest slab. The units above 250 are charged at 6.50, and then they are removed from $units.
• The same is done for the 151 to 250 slab and the 51 to 150 slab. The remaining units are charged at 3.50.
• For 320 units: 70 x 6.50 + 100 x 5.20 + 100 x 4.00 + 50 x 3.50 = 1550.
• number_format() shows the amount with 2 decimals and a thousands separator.

Write a simple calculator program in PHP using switch case

Description: Write a simple calculator program in PHP using the switch case.

Rules and hints:

• Operations: addition, subtraction, multiplication and division.
• Use an HTML form with two number fields and a select box for the operation.
• Check that both values are numbers, and do not allow division by zero.

PHP simple calculator program

<?php
$result = "";

if ($_SERVER["REQUEST_METHOD"] === "POST") {
    $first = $_POST["first_num"] ?? "";
    $second = $_POST["second_num"] ?? "";
    $operator = $_POST["operator"] ?? "";

    if (is_numeric($first) && is_numeric($second)) {
        switch ($operator) {
            case "Add":
                $result = $first + $second;
                break;
            case "Subtract":
                $result = $first - $second;
                break;
            case "Multiply":
                $result = $first * $second;
                break;
            case "Divide":
                $result = ($second == 0) ? "Cannot divide by zero" : $first / $second;
                break;
            default:
                $result = "Please select an operation";
        }
    } else {
        $result = "Please enter valid numbers";
    }
}
?>
<form method="post">
    <input type="text" name="first_num" value="<?php echo htmlspecialchars($_POST["first_num"] ?? ""); ?>">
    <select name="operator">
        <option>Add</option>
        <option>Subtract</option>
        <option>Multiply</option>
        <option>Divide</option>
    </select>
    <input type="text" name="second_num" value="<?php echo htmlspecialchars($_POST["second_num"] ?? ""); ?>">
    <button type="submit">Calculate</button>
</form>
<?php
if ($result !== "") {
    echo "<p>Result: " . htmlspecialchars((string) $result) . "</p>";
}
?>

Output:

How it works

• The PHP code at the top runs only when the form is sent with POST.
• is_numeric() checks both values before the calculation.
• switch selects the operation using the text of the select box.
• The old values are put back in the fields, and htmlspecialchars() keeps the page safe from XSS.

Related: PHP Forms Handling.

Write a PHP program to check whether a number is positive, negative or zero

Description: Write a PHP program to check whether a number is positive, negative or zero.

Rules and hints:

• Use if else conditions.
• Use the correct PHP operators.
• Also check that the value is a number.
• Write the logic in a function, so you can test many values.

PHP program to check a positive, negative or zero number

<?php
function checkNumber($number) {
    if (!is_numeric($number)) {
        return "Please enter a number";
    }

    if ($number > 0) {
        return $number . " is a positive number";
    } elseif ($number < 0) {
        return $number . " is a negative number";
    }

    return "The number is zero";
}

echo checkNumber(324) . "<br>";
echo checkNumber(-15) . "<br>";
echo checkNumber(0) . "<br>";
echo checkNumber("abc");
?>

Output:

How it works

• is_numeric() checks that the value is a number, so text like “abc” is rejected first.
• If the number is bigger than 0 it is positive, if it is smaller than 0 it is negative. The only remaining case is zero.
• Because it is a function, you can call it with different values.