Function declaration and calling in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function in PHP?

A function is a reusable block of code that performs a specific task. You can call it whenever you need that task done.

beginner

How do you declare a function in PHP?

Use the <code>function</code> keyword, followed by the function name and parentheses. Inside curly braces, write the code to run when the function is called.<br><br>Example:<br><code>function greet() { echo 'Hello!'; }</code>

beginner

How do you call a function in PHP?

Write the function name followed by parentheses. If the function needs inputs, put them inside the parentheses.

Example:
greet();

beginner

What happens if you call a function that has parameters?

You must provide the required values (arguments) inside the parentheses when calling the function. These values are used inside the function.<br><br>Example:<br><code>function sayHello($name) { echo "Hello, $name!"; }<br>sayHello('Alice');</code>

beginner

Can a function return a value in PHP? How?

Yes, a function can send back a value using the <code>return</code> keyword. This lets you use the result elsewhere.<br><br>Example:<br><code>function add($a, $b) { return $a + $b; }<br>$sum = add(3, 4);</code>

Which keyword is used to declare a function in PHP?

A function

B def

C func

D declare

In PHP, the keyword function is used to declare a function.

How do you call a function named greet in PHP?

A call greet();

B run greet();

C function greet();

D greet();

To call a function, just write its name followed by parentheses: greet();

What will this code output?

function sayHi() { echo 'Hi!'; }
sayHi();

A Error

B sayHi

C Hi!

D Nothing

The function sayHi prints 'Hi!' when called.

What is needed when calling a function that requires parameters?

A Nothing, just call it

B Provide the required arguments inside parentheses

C Declare the function again

D Use return keyword

You must provide the required arguments inside parentheses when calling a function with parameters.

What does the return keyword do in a function?

A Sends a value back to where the function was called

B Prints a message

C Stops the program

D Declares a variable

The return keyword sends a value back to the place where the function was called.

Explain how to declare and call a function in PHP with an example.

Think about the basic structure and how you use the function after declaring it.

Describe how parameters and return values work in PHP functions.

Consider how data goes into and comes out of a function.

Practice

1. What is the correct way to declare a function named greet in PHP?

easy

A. function greet() { }

B. def greet() { }

C. func greet() { }

D. function: greet() { }

Solution

1. Step 1: Recognize PHP function declaration syntax

   In PHP, functions are declared using the keyword function followed by the function name and parentheses.

2. Step 2: Match the correct syntax

   function greet() { } uses function greet() { }, which is the correct PHP syntax for declaring a function named greet.

3. Final Answer:

   function greet() { } -> Option A

4. Quick Check:

   PHP function declaration = function greet() { } [OK]

Hint: Use 'function' keyword to declare functions in PHP [OK]

Common Mistakes:

• Using 'def' instead of 'function'
• Adding a colon after 'function'
• Using 'func' keyword which is not valid in PHP

2. Which of the following is the correct way to call a function named sayHello in PHP?

easy

A. call sayHello();

B. sayHello();

C. sayHello;

D. callFunction(sayHello);

Solution

1. Step 1: Understand PHP function call syntax

   In PHP, to call a function, you write the function name followed by parentheses, optionally with arguments inside.

2. Step 2: Identify the correct option

   sayHello(); uses sayHello();, which is the correct way to call the function named sayHello.

3. Final Answer:

   sayHello(); -> Option B

4. Quick Check:

   Function call syntax = sayHello(); [OK]

Hint: Call functions by name with parentheses () [OK]

Common Mistakes:

• Using 'call' keyword which does not exist in PHP
• Omitting parentheses when calling functions
• Using incorrect function call syntax like callFunction()

3. What will be the output of the following PHP code?

function add($a, $b) {
    return $a + $b;
}
echo add(3, 4);

medium

A. 7

B. 34

C. add(3, 4)

D. Error

Solution

1. Step 1: Understand the function behavior

   The function add takes two parameters and returns their sum.

2. Step 2: Calculate the return value

   Calling add(3, 4) returns 3 + 4 = 7, which is then printed by echo.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Functions return values; echo prints the result [OK]

Common Mistakes:

• Concatenating numbers as strings instead of adding
• Expecting function name to print instead of return value
• Syntax errors from missing semicolons

4. Identify the error in the following PHP code:

function greet() {
    echo "Hello!";
}
greet;

medium

A. Missing semicolon after function declaration

B. Function name is incorrect

C. Missing parentheses when calling the function

D. Echo statement syntax error

Solution

1. Step 1: Check function call syntax

   The function greet is declared correctly, but when calling it, parentheses are missing.

2. Step 2: Understand PHP function call requirements

   In PHP, functions must be called with parentheses, even if they take no arguments. So greet; is invalid; it should be greet();.

3. Final Answer:

   Missing parentheses when calling the function -> Option C

4. Quick Check:

   Function calls need () even if no arguments [OK]

Hint: Always use () to call functions, even if empty [OK]

Common Mistakes:

• Calling functions without parentheses
• Confusing function declaration with call
• Missing semicolons elsewhere

5. Consider the following PHP code:

function multiply($x, $y = 2) {
    return $x * $y;
}
echo multiply(5);

What will be the output and why?

hard

A. 0 because default value is ignored

B. 5 because only one argument is passed

C. Error because both parameters are required

D. 10 because the second parameter uses default value 2

Solution

1. Step 1: Understand default parameter usage

   The function multiply has two parameters, where $y has a default value of 2.

2. Step 2: Analyze the function call

   Calling multiply(5) passes 5 as $x, and since $y is not provided, it uses the default 2.

3. Step 3: Calculate the result

   The function returns 5 * 2 = 10, which is printed by echo.

4. Final Answer:

   10 because the second parameter uses default value 2 -> Option D

5. Quick Check:

   5 * 2 = 10 with default parameter [OK]

Hint: Default parameters fill missing arguments automatically [OK]

Common Mistakes:

• Assuming all parameters must be passed
• Ignoring default values
• Expecting error when missing arguments