Switch statement execution in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a switch statement in PHP?

A switch statement allows you to execute different blocks of code based on the value of a single expression. It helps to replace multiple if-else statements for cleaner code.

beginner

How does PHP decide which case to execute in a switch statement?

PHP compares the value of the switch expression with each case value using loose comparison (==). When a match is found, it executes that case's code.

intermediate

What happens if you forget to add a break statement at the end of a case block?

If you omit break, PHP will continue executing the next case(s) even if they don't match. This is called "fall-through" and can cause unexpected behavior.

beginner

What is the role of the default case in a switch statement?

The default case runs if none of the other cases match the expression. It acts like the "else" part of an if-else chain.

intermediate

Can a switch statement in PHP handle multiple cases with the same code block? How?

Yes. You can list multiple case labels one after another without break between them, so they share the same code block.

What keyword stops execution from falling through to the next case in a PHP switch statement?

A break

B continue

C stop

D exit

The break keyword ends the current case and prevents execution from continuing to the next case.

If no case matches and there is no default case, what happens in a PHP switch statement?

A An error is thrown

B The first case executes

C The switch block is skipped

D The last case executes

If no case matches and no default is provided, PHP skips the entire switch block.

How does PHP compare the switch expression to case values?

A Strict comparison (===)

B By converting to strings

C By reference

D Loose comparison (==)

PHP uses loose comparison (==) to match the switch expression with case values.

Which of the following is true about the default case in a switch statement?

A It must be the last case

B It runs only if no other case matches

C It runs before any case

D It is optional and ignored if present

The default case runs only if no other case matches the switch expression.

What happens if you list multiple case labels without breaks between them?

A All those cases share the same code block

B PHP throws a syntax error

C Only the last case runs

D Only the first case runs

Multiple case labels without breaks share the same code block, allowing grouped cases.

Explain how a PHP switch statement executes when a matching case is found. Include what happens if there is no break.

Think about how PHP moves through cases after a match.

Describe the role and importance of the default case in a PHP switch statement.

Consider what happens when no case matches.

Practice

1. What does a switch statement do in PHP?

easy

A. It chooses which code to run based on a value.

B. It repeats code multiple times.

C. It defines a function.

D. It creates a new variable.

Solution

1. Step 1: Understand the purpose of switch

   A switch statement compares a value to multiple cases to decide which code block to run.

2. Step 2: Compare with other options

   Repeating code is done by loops, functions define reusable code, and variables store data, so these are not correct.

3. Final Answer:

   It chooses which code to run based on a value. -> Option A

4. Quick Check:

   Switch selects code by value = A [OK]

Hint: Switch picks code by matching value quickly [OK]

Common Mistakes:

• Confusing switch with loops
• Thinking switch defines functions
• Believing switch creates variables

2. Which of the following is the correct syntax to start a switch statement in PHP?

easy

A. switch [variable] {

B. switch variable {

C. switch (variable) {

D. switch variable() {

Solution

1. Step 1: Recall switch syntax

   In PHP, switch requires parentheses around the variable: switch (variable) {

2. Step 2: Check other options

   Options without parentheses or with brackets or parentheses after variable name are invalid syntax.

3. Final Answer:

   switch (variable) { -> Option C

4. Quick Check:

   Switch uses parentheses around variable [OK]

Hint: Switch always uses parentheses around the variable [OK]

Common Mistakes:

• Omitting parentheses
• Using square brackets instead of parentheses
• Adding parentheses after variable name

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

 $color = 'red';
 switch ($color) {
   case 'blue':
     echo 'Blue color';
     break;
   case 'red':
     echo 'Red color';
     break;
   default:
     echo 'No color';
 }

medium

A. Blue color

B. Syntax error

C. No color

D. Red color

Solution

1. Step 1: Check the value of $color

   $color is set to 'red'.

2. Step 2: Match cases in switch

   The switch checks 'blue' first (no match), then 'red' (match), so it runs echo 'Red color' and breaks.

3. Final Answer:

   Red color -> Option D

4. Quick Check:

   Value 'red' matches case 'red' [OK]

Hint: Match value to case, break stops further checks [OK]

Common Mistakes:

• Forgetting break causes fall-through
• Assuming default runs even if case matches
• Mixing case values

4. Identify the error in this PHP switch code:

 $day = 3;
 switch ($day) {
   case 1:
     echo 'Monday';
   case 2:
     echo 'Tuesday';
     break;
   default:
     echo 'Other day';
 }

medium

A. Missing break after case 1 causes fall-through.

B. Switch statement syntax is incorrect.

C. Variable $day is not defined.

D. Default case should be first.

Solution

1. Step 1: Check breaks in cases

   Case 1 has no break, so if matched, it falls through to case 2.

2. Step 2: Understand effect of missing break

   Missing break causes code for case 2 to run even if case 1 matches, which is usually unintended.

3. Final Answer:

   Missing break after case 1 causes fall-through. -> Option A

4. Quick Check:

   Break missing after case 1 causes fall-through [OK]

Hint: Always add break after each case to avoid fall-through [OK]

Common Mistakes:

• Ignoring missing break causes multiple cases to run
• Thinking default must be first
• Assuming variable is undefined

5. Given this PHP code, what will be the output?

 $score = 85;
 switch (true) {
   case ($score >= 90):
     echo 'Grade A';
     break;
   case ($score >= 80):
     echo 'Grade B';
     break;
   case ($score >= 70):
     echo 'Grade C';
     break;
   default:
     echo 'Fail';
 }

hard

A. Grade A

B. Grade B

C. Grade C

D. Fail

Solution

1. Step 1: Understand switch(true) usage

   The switch compares true to each case condition result.

2. Step 2: Evaluate each case condition

   $score is 85, so ($score >= 90) is false, ($score >= 80) is true, so it matches case 2 and prints 'Grade B'.

3. Final Answer:

   Grade B -> Option B

4. Quick Check:

   Switch(true) matches first true case = Grade B [OK]

Hint: Use switch(true) to check conditions in order [OK]

Common Mistakes:

• Expecting switch to compare values directly
• Not understanding switch(true) trick
• Missing break causing fall-through