Switch statement in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a switch statement used for in C++?

A switch statement lets you choose between many options based on the value of a single variable. It helps run different code blocks depending on that value.

beginner

How do you write a basic switch statement syntax in C++?

You write switch(variable) { case value1: //code break; case value2: //code break; default: //code }. Each case checks if the variable matches a value, and break stops the code from running into the next case.

intermediate

What happens if you forget to put break in a case inside a switch?

If you forget break, the program will continue running the next cases too, even if their values don't match. This is called "fall-through." Sometimes it's useful, but often it causes bugs.

beginner

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

The default case runs if none of the other case values match the variable. It's like an "else" to catch all other possibilities.

intermediate

Can switch statements in C++ work with strings?

No, C++ switch statements only work with integral types like int, char, or enums. For strings, you need to use if-else chains.

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

A break

B continue

C stop

D exit

The break keyword ends the current case and prevents running the next cases.

Which part of a switch runs if no cases match?

A case 0

B else

C final

D default

The default case runs when no other case matches the variable.

Can you use a switch statement with a float variable in C++?

A No, only integral types

B Yes, always

C Only with <code>break</code>

D Only if you cast it to int

C++ switch only works with integral types like int or char, not float.

What happens if you omit break in a case?

A Program crashes

B Runs next case(s) too

C Skips to default

D Compiler error

Without break, execution continues into the next case(s), called fall-through.

Which of these is a valid switch variable type?

A string

B double

C char

D float

Only integral types like char can be used in switch statements.

Explain how a switch statement works and why break is important.

Think of a menu where you pick one option and stop.

Describe when you would use a switch instead of if-else statements.

Imagine choosing from many fixed choices quickly.

Practice

1. What is the main purpose of a switch statement in C++?

easy

A. To declare a variable

B. To repeat a block of code multiple times

C. To define a function

D. To choose which block of code to run based on a single value

Solution

1. Step 1: Understand the role of switch

   A switch statement checks one value and runs code matching that value.

2. Step 2: Compare with other options

   Repeating code is done by loops, functions define reusable code, and variables store data.

3. Final Answer:

   To choose which block of code to run based on a single value -> Option D

4. Quick Check:

   Switch selects code by value = A [OK]

Hint: Switch picks code based on one value quickly [OK]

Common Mistakes:

• Confusing switch with loops
• Thinking switch defines functions
• Mixing switch with variable declaration

2. Which of the following is the correct syntax to start a switch statement for variable choice?

easy

A. switch(choice) {

B. switch choice {

C. switch choice() {

D. switch(choice);

Solution

1. Step 1: Recall switch syntax

   The switch statement requires parentheses around the variable: switch(variable).

2. Step 2: Check each option

   switch(choice) { uses correct parentheses and opening brace. Others miss parentheses or use wrong punctuation.

3. Final Answer:

   switch(choice) { -> Option A

4. Quick Check:

   Correct switch syntax uses parentheses [OK]

Hint: Switch needs parentheses around variable [OK]

Common Mistakes:

• Omitting parentheses
• Using semicolon instead of brace
• Adding parentheses after variable name

3. What will be the output of this code?

int x = 2;
switch(x) {
  case 1:
    std::cout << "One";
    break;
  case 2:
    std::cout << "Two";
    break;
  default:
    std::cout << "Other";
}

medium

A. One

B. Two

C. Other

D. No output

Solution

1. Step 1: Check the value of x

   The variable x is 2.

2. Step 2: Match case in switch

   The switch matches case 2, so it prints "Two" and then breaks.

3. Final Answer:

   Two -> Option B

4. Quick Check:

   Value 2 matches case 2 = Two [OK]

Hint: Match variable value to case label [OK]

Common Mistakes:

• Forgetting break causes fall-through
• Choosing default when case matches
• Confusing output with case number

4. Identify the error in this switch statement:

int n = 3;
switch(n) {
  case 1:
    std::cout << "One";
  case 2:
    std::cout << "Two";
    break;
  default:
    std::cout << "Default";
}

medium

A. default case must be last

B. Variable n should be a string

C. Missing break after case 1 causes fall-through

D. case labels must be strings

Solution

1. Step 1: Check case 1 block

   There is no break; after case 1, so execution falls through to case 2.

2. Step 2: Understand consequences

   Without break, both "One" and "Two" print if n=1. This is usually unintended.

3. Final Answer:

   Missing break after case 1 causes fall-through -> Option C

4. Quick Check:

   Break prevents fall-through = A [OK]

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

Common Mistakes:

• Forgetting break causes multiple outputs
• Thinking default must be last (it can be anywhere)
• Believing case labels must be strings

5. You want to write a switch statement that prints "Weekend" for cases 6 and 7, and "Weekday" for cases 1 to 5. Which code snippet correctly does this?

hard

A. switch(day) {
case 1: case 2: case 3: case 4: case 5:
std::cout << "Weekday";
break;
case 6: case 7:
std::cout << "Weekend";
break;
default:
std::cout << "Invalid";
}

B. switch(day) {
case 1:
case 2:
case 3:
case 4:
case 5:
std::cout << "Weekend";
break;
case 6:
case 7:
std::cout << "Weekday";
break;
default:
std::cout << "Invalid";
}

C. switch(day) {
case 1:
case 2:
case 3:
case 4:
case 5:
std::cout << "Weekday";
case 6:
case 7:
std::cout << "Weekend";
break;
default:
std::cout << "Invalid";
}

D. switch(day) {
case 1: case 2: case 3: case 4: case 5:
std::cout << "Weekend";
case 6: case 7:
std::cout << "Weekday";
break;
default:
std::cout << "Invalid";
}

Solution

1. Step 1: Group cases for weekdays and weekends

   Cases 1 to 5 print "Weekday"; cases 6 and 7 print "Weekend". Grouping cases with no code between them is correct.

2. Step 2: Check breaks and outputs

   switch(day) { case 1: case 2: case 3: case 4: case 5: std::cout << "Weekday"; break; case 6: case 7: std::cout << "Weekend"; break; default: std::cout << "Invalid"; } groups cases correctly and uses breaks to prevent fall-through. Others mix outputs or miss breaks.

3. Final Answer:

   Option A code correctly prints "Weekday" for 1-5 and "Weekend" for 6-7 -> Option A

4. Quick Check:

   Group cases + breaks = correct switch [OK]

Hint: Group cases without code, add break after each group [OK]

Common Mistakes:

• Missing breaks causing fall-through
• Swapping outputs for cases
• Not grouping cases properly