$_POST for form submissions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using $_POST?

Consider a form submission where the form sends a POST request with a field named 'username' set to 'Alice'. What will this PHP code output?

PHP

<?php
if (isset($_POST['username'])) {
    echo "Hello, " . $_POST['username'] . "!";
} else {
    echo "No username provided.";
}
?>

A Undefined index: username

B No username provided.

C Hello, !

D Hello, Alice!

💡 Hint

Remember that $_POST contains data sent by the form using the POST method.

If the form sends 'username' with value 'Alice', then $_POST['username'] is set and the code prints 'Hello, Alice!'.

🧠 Conceptual

intermediate

Which statement about $_POST is true?

Choose the correct statement about the PHP $_POST superglobal array.

A $_POST contains data sent via the HTTP POST method.

B $_POST contains data sent via the HTTP GET method.

C $_POST is used to store session variables.

D $_POST is an object that holds form data.

💡 Hint

Think about how form data is sent using different HTTP methods.

$_POST is an associative array that holds data sent by forms using the POST method.

🔧 Debug

advanced

Why does this PHP code produce an error when accessing $_POST?

What error will this code produce and why?

PHP

<?php
echo $_POST['email'];
?>

A Syntax error because $_POST is not defined.

B Fatal error: Cannot access $_POST directly.

C Undefined index: email if the form did not send 'email'.

D No output because $_POST is empty but no error.

💡 Hint

What happens if you try to access an array key that does not exist?

Accessing $_POST['email'] when 'email' is not sent causes a PHP notice: Undefined index.

📝 Syntax

advanced

Which option correctly checks if a POST field 'age' is set and not empty?

Select the correct PHP code snippet that safely checks if the 'age' field was submitted and is not empty.

A if (isset($_POST['age']) || $_POST['age'] != '') { echo 'Age is set'; }

B if (isset($_POST['age']) && $_POST['age'] !== '') { echo 'Age is set'; }

C if ($_POST['age']) { echo 'Age is set'; }

D if (!empty($_POST['age'])) { echo 'Age is set'; } else { echo 'Age not set'; }

💡 Hint

Use isset() to check if the key exists and compare to empty string to ensure it's not empty.

Option B correctly uses isset() to check existence and compares to empty string to ensure value is not empty.

🚀 Application

expert

How many items are in $_POST after submitting this form?

Given this HTML form submitted via POST:

How many key-value pairs will $_POST contain after submission?

A 1

B 3

C 2

D 0

💡 Hint

Checkboxes only send their value if checked. Multiple inputs with the same name overwrite or combine values.

Only 'first', 'last', and 'subscribe' fields are sent. Since only one 'subscribe' checkbox is checked, $_POST has keys 'first', 'last', and 'subscribe'. So 3 keys. But since 'subscribe' checkboxes share the same name, only one value is sent for 'subscribe'. So total keys: 3.