Switch statement in C++ - Mini Project: Build & Apply

Using a Switch Statement in C++

📖 Scenario: You are creating a simple program that tells the name of a day based on a number input from 1 to 7. Each number corresponds to a day of the week.

🎯 Goal: Build a program that uses a switch statement to print the correct day name for a given number.

📋 What You'll Learn

Create an integer variable called dayNumber with a value from 1 to 7

Create a switch statement that checks dayNumber

Use case labels for numbers 1 through 7, each printing the correct day name

Include a default case that prints "Invalid day number"

Print the day name or the invalid message as the final output

💡 Why This Matters

🌍 Real World

Switch statements are used in many programs to choose actions based on a value, like menu selections or commands.

💼 Career

Understanding switch statements helps in writing clear and efficient code for decision-making in software development.

1

Create the day number variable

Create an integer variable called dayNumber and set it to 3.

C++

// Create an integer variable called dayNumber and set it to 3
// Your code here

Hint

Use int dayNumber = 3; to create the variable.

2

Start the switch statement

Write a switch statement that checks the variable dayNumber.

C++

int dayNumber = 3;

// Start a switch statement on dayNumber
// Your code here

Hint

Use switch(dayNumber) { } to start the switch.

3

Add cases for days 1 to 7

Inside the switch(dayNumber), add case labels for numbers 1 to 7. For each case, write a cout << "Monday" << endl; statement to print the day name (e.g., "Monday" for 1). Add a break; after each print statement. Also add a default case that prints "Invalid day number". Make sure to include #include <iostream> and using namespace std; later.

C++

int dayNumber = 3;

switch(dayNumber) {
    // Add cases 1 to 7 with cout and break
    // Add default case with cout
    // Your code here
}

Hint

Each case should print the correct day with cout << "Day" << endl; and end with break;. The default prints the invalid message.

4

Run the program to see the output

Add the necessary includes, namespace, and main function to run the program. The output should be Wednesday.

C++

#include 
using namespace std;

int main() {
    int dayNumber = 3;

    switch(dayNumber) {
        case 1:
            cout << "Monday" << endl;
            break;
        case 2:
            cout << "Tuesday" << endl;
            break;
        case 3:
            cout << "Wednesday" << endl;
            break;
        case 4:
            cout << "Thursday" << endl;
            break;
        case 5:
            cout << "Friday" << endl;
            break;
        case 6:
            cout << "Saturday" << endl;
            break;
        case 7:
            cout << "Sunday" << endl;
            break;
        default:
            cout << "Invalid day number" << endl;
    }

    // Run the program
    return 0;
}

Hint

Ensure #include <iostream> and using namespace std; are at the top, and return 0; at the end of main().

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