Foreach loop for arrays in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a foreach loop used for in PHP?

A foreach loop is used to easily go through each item in an array, one by one, without needing to know the array's size.

beginner

How do you write a basic foreach loop to print all values in an array named $fruits?

foreach ($fruits as $fruit) { echo $fruit; }

intermediate

What does this code do?
foreach ($colors as $key => $value) { echo "$key: $value"; }

It goes through the $colors array and prints each key and its matching value, like 'red: #ff0000'.

intermediate

Can you modify array values inside a foreach loop in PHP?

Yes, but you must use a reference by adding & before the value variable, like: foreach ($arr as &$value) { $value = $value * 2; }

beginner

What happens if you use foreach on an empty array?

The loop does not run at all because there are no items to go through.

Which keyword starts a foreach loop in PHP?

A for

B foreach

C while

D loop

The foreach keyword is used specifically to loop through arrays in PHP.

How do you access the key and value inside a foreach loop?

A foreach ($array as $key => $value)

B foreach ($array as $value => $key)

C foreach ($array as $value)

D foreach ($array as $key)

The correct syntax to get both key and value is foreach ($array as $key => $value).

What will this code output?
$nums = [1, 2, 3]; foreach ($nums as $n) { echo $n; }

A 123

B 1 2 3

C Array

D Error

The loop prints each number one after another without spaces, so output is '123'.

How do you change values inside a foreach loop?

A You cannot change values in foreach

B Use $GLOBALS

C Use & before the value variable

D Use a for loop instead

Adding & before the value variable lets you modify the original array values inside the loop.

What happens if the array is empty in a foreach loop?

A It runs infinitely

B It runs once with null

C It throws an error

D The loop does not run

If the array is empty, foreach simply skips the loop body.

Explain how a foreach loop works with arrays in PHP.

Think about how you would tell a friend to read each item in a list one by one.

Describe how to modify array values inside a foreach loop and why you need a reference.

Imagine you want to change the original list items, not just copies.

Practice

1. What does the foreach loop do in PHP when used with an array?

easy

A. It only visits the first item in the array.

B. It visits each item in the array one by one.

C. It deletes all items in the array.

D. It reverses the order of the array.

Solution

1. Step 1: Understand the purpose of foreach

   The foreach loop is designed to go through each element in an array, one at a time.

2. Step 2: Compare options with foreach behavior

   Only It visits each item in the array one by one. correctly describes visiting each item. Others describe actions foreach does not perform.

3. Final Answer:

   It visits each item in the array one by one. -> Option B

4. Quick Check:

   foreach loops visit all items [OK]

Hint: Remember: foreach loops through all array items [OK]

Common Mistakes:

• Thinking foreach only visits first item
• Confusing foreach with array modification functions
• Assuming foreach changes array order

2. Which of the following is the correct syntax to loop through an array $colors using foreach to get each value?

easy

A. foreach ($colors in $color) { echo $color; }

B. foreach $colors as $color { echo $color; }

C. foreach ($colors as $color) { echo $color; }

D. foreach ($color as $colors) { echo $color; }

Solution

1. Step 1: Identify correct foreach syntax

   The correct syntax is: foreach (array as value) { ... } with parentheses and 'as' keyword.

2. Step 2: Check each option

   foreach ($colors as $color) { echo $color; } matches correct syntax. Options A, B, and D have syntax errors or wrong order.

3. Final Answer:

   foreach ($colors as $color) { echo $color; } -> Option C

4. Quick Check:

   Correct foreach syntax uses 'foreach (array as value)' [OK]

Hint: Use parentheses and 'as' keyword in foreach [OK]

Common Mistakes:

• Missing parentheses around array and variable
• Using 'in' instead of 'as'
• Swapping variable and array positions

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

$fruits = ['apple', 'banana', 'cherry'];
foreach ($fruits as $fruit) {
    echo $fruit . ' ';
}

medium

A. apple banana cherry

B. apple, banana, cherry

C. Array

D. applebanana cherry

Solution

1. Step 1: Understand the loop output

   The foreach loop prints each fruit followed by a space.

2. Step 2: Combine printed values

   Output will be 'apple ' then 'banana ' then 'cherry ' concatenated.

3. Final Answer:

   apple banana cherry -> Option A

4. Quick Check:

   Each fruit printed with space [OK]

Hint: Look for spaces after each echo in loop [OK]

Common Mistakes:

• Expecting commas instead of spaces
• Thinking array prints as string
• Missing spaces between words

4. Find the error in this PHP code snippet:

$numbers = [1, 2, 3];
foreach ($numbers $num) {
    echo $num;
}

medium

A. Missing 'as' keyword in foreach loop.

B. Array should be a string.

C. Variable $num is not defined.

D. Echo statement is incorrect.

Solution

1. Step 1: Check foreach syntax

   foreach requires 'as' keyword between array and variable.

2. Step 2: Identify missing keyword

   The code misses 'as' between $numbers and $num, causing syntax error.

3. Final Answer:

   Missing 'as' keyword in foreach loop. -> Option A

4. Quick Check:

   foreach needs 'as' keyword [OK]

Hint: Always include 'as' in foreach syntax [OK]

Common Mistakes:

• Omitting 'as' keyword
• Confusing variable and array order
• Assuming variables need prior declaration

5. Given the array $items = ['a' => 1, 'b' => 0, 'c' => 3, 'd' => null];, which foreach loop will print only keys with truthy values?

hard

A. foreach ($items as $key => $value) { echo $key; }

B. foreach ($items as $key => $value) { if ($value === 0) echo $key; }

C. foreach ($items as $value) { if ($value) echo $value; }

D. foreach ($items as $key => $value) { if ($value) echo $key; }

Solution

1. Step 1: Understand truthy values in PHP

   Values like 1 and 3 are truthy; 0 and null are falsy.

2. Step 2: Analyze each loop's condition

   foreach ($items as $key => $value) { if ($value) echo $key; } prints keys only if value is truthy, matching requirement. Others print keys regardless or check wrong condition.

3. Final Answer:

   foreach ($items as $key => $value) { if ($value) echo $key; } -> Option D

4. Quick Check:

   Check value truthiness before echo key [OK]

Hint: Use if ($value) to filter truthy values [OK]

Common Mistakes:

• Printing keys without condition
• Checking for zero instead of truthy
• Not using key => value syntax