Function declaration and calling in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a function with default parameter

What is the output of this PHP code?

PHP

<?php
function greet($name = "Guest") {
    return "Hello, $name!";
}
echo greet();
?>

A Hello, name!

B Hello, !

C Hello, Guest!

D Syntax Error

💡 Hint

Check the default value of the parameter in the function.

The function greet has a default parameter 'Guest'. When called without arguments, it returns 'Hello, Guest!'.

❓ Predict Output

intermediate

Return value from a function call

What will be the output of this PHP code?

PHP

<?php
function add($a, $b) {
    return $a + $b;
}
$result = add(5, 3);
echo $result;
?>

A 5 + 3

B 53

C Error: Undefined function

D 8

💡 Hint

The function returns the sum of two numbers.

The function add returns the sum of 5 and 3, which is 8.

🔧 Debug

advanced

Identify the error in function call

What error will this PHP code produce?

PHP

<?php
function multiply($x, $y) {
    return $x * $y;
}
echo multiply(4);
?>

A Warning: Missing argument 2 for multiply()

B Fatal error: Call to undefined function multiply()

C Output: 4

D No output, code runs fine

💡 Hint

Check how many arguments the function expects and how many are given.

The function multiply expects 2 arguments but only 1 is given, causing a warning about missing argument.

❓ Predict Output

advanced

Output of recursive function

What is the output of this PHP code?

PHP

<?php
function factorial($n) {
    if ($n <= 1) {
        return 1;
    } else {
        return $n * factorial($n - 1);
    }
}
echo factorial(4);
?>

A 24

B 10

C Error: Maximum function nesting level reached

D 4

💡 Hint

Factorial of 4 is 4*3*2*1.

The recursive function calculates factorial correctly. 4*3*2*1 = 24.

🧠 Conceptual

expert

Function variable scope behavior

What will be the output of this PHP code?

PHP

<?php
$x = 10;
function test() {
    $x = 5;
    echo $x . ' ';
}
test();
echo $x;
?>

A 10 10

B 5 10

C 5 5

D 10 5

💡 Hint

Variables inside functions have their own scope unless declared global.

Inside the function, $x is 5 (local). Outside, $x remains 10 (global). So output is '5 10'.

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