Switch statement - 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.

🎯 Goal: Build a C 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 the value 3

Create an integer variable called invalidDay with the value 0

Use a switch statement on dayNumber with cases for numbers 1 to 7

Print the correct day name for each case

Use default case to print "Invalid day" if the number is not 1 to 7

Print the result using printf

💡 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

# Your code here

Hint

Use int dayNumber = 3; to create the variable.

2

Create the invalid day variable

Create an integer variable called invalidDay and set it to 0.

C

int dayNumber = 3;
# Your code here

Hint

Use int invalidDay = 0; to create the variable.

3

Write the switch statement for day names

Write a switch statement using dayNumber with cases 1 to 7. For each case, use printf to print the day name: 1 for "Monday", 2 for "Tuesday", 3 for "Wednesday", 4 for "Thursday", 5 for "Friday", 6 for "Saturday", 7 for "Sunday". Add a default case that prints "Invalid day".

C

int dayNumber = 3;
int invalidDay = 0;

# Your code here

Hint

Use switch(dayNumber) { ... } with case labels and break; after each printf.

4

Print the day name result

Run the program to print the day name for dayNumber. The output should be Wednesday.

C

int dayNumber = 3;
int invalidDay = 0;

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

# No extra code needed, just run the program

Hint

Compile and run the program. It should print Wednesday.

Practice

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

easy

A. To define a function

B. To repeat a block of code multiple times

C. To select one action from multiple choices based on a variable's value

D. To declare variables

Solution

1. Step 1: Understand the role of switch

   A switch statement chooses one path among many based on a variable's value.

2. Step 2: Compare with other options

   Loops repeat code, functions define reusable blocks, and declarations create variables, which are different from switch's purpose.

3. Final Answer:

   To select one action from multiple choices based on a variable's value -> Option C

4. Quick Check:

   Switch = Choice selection [OK]

Hint: Switch picks one case based on value, like a menu choice [OK]

Common Mistakes:

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

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

easy

A. switch (variable) { case 1: ... }

B. switch variable { case 1: ... }

C. switch [variable] { case 1: ... }

D. switch variable: case 1: ...

Solution

1. Step 1: Recall switch syntax

   The correct syntax uses parentheses around the variable: switch(variable) { ... }

2. Step 2: Check options

   Only switch (variable) { case 1: ... } uses parentheses correctly; others miss parentheses or use wrong brackets.

3. Final Answer:

   switch (variable) { case 1: ... } -> Option A

4. Quick Check:

   Switch needs parentheses around variable [OK]

Hint: Remember: switch(variable) uses parentheses, not brackets or none [OK]

Common Mistakes:

• Omitting parentheses around variable
• Using square brackets instead of parentheses
• Using colon instead of braces

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

int x = 2;
switch (x) {
  case 1:
    printf("One\n");
    break;
  case 2:
    printf("Two\n");
    break;
  default:
    printf("Other\n");
}

medium

A. One

B. Other

C. No output

D. Two

Solution

1. Step 1: Identify the switch variable value

   The variable x is 2, so the switch checks case 2.

2. Step 2: Match case and output

   Case 2 matches, so it prints "Two" and then breaks to stop further checks.

3. Final Answer:

   Two -> Option D

4. Quick Check:

   Case 2 matches x=2, prints "Two" [OK]

Hint: Match variable value to case, print and break [OK]

Common Mistakes:

• Forgetting break causes fall-through
• Choosing default when case matches
• Confusing case numbers

4. Find the error in this switch statement:

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

medium

A. Missing break after case 1

B. Missing default case

C. Wrong switch syntax

D. Variable n not declared

Solution

1. Step 1: Check each case for break

   Case 1 lacks a break, so if matched, it would fall through to case 2.

2. Step 2: Understand impact

   Missing break can cause unintended multiple prints; adding break after case 1 fixes this.

3. Final Answer:

   Missing break after case 1 -> Option A

4. Quick Check:

   Each case needs break to stop fall-through [OK]

Hint: Always add break after each case unless fall-through wanted [OK]

Common Mistakes:

• Ignoring missing break causes fall-through
• Thinking default is mandatory
• Assuming variable declaration error

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 correctly does this?

hard

A. switch(day) { case 1: printf("Weekday\n"); break; case 2: printf("Weekday\n"); break; case 3: printf("Weekend\n"); break; case 4: printf("Weekday\n"); break; case 5: printf("Weekday\n"); break; case 6: printf("Weekend\n"); break; case 7: printf("Weekend\n"); break; }

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

C. switch(day) { case 1: case 2: case 3: case 4: case 5: printf("Weekend\n"); break; case 6: case 7: printf("Weekday\n"); break; }

D. switch(day) { case 1: case 2: case 3: case 4: case 5: printf("Weekday\n"); case 6: case 7: printf("Weekend\n"); break; }

Solution

1. Step 1: Group cases for same output

   Cases 1 to 5 print "Weekday", so group them before one printf and break.

2. Step 2: Group weekend cases

   Cases 6 and 7 print "Weekend" similarly grouped with break.

3. Step 3: Check default case

   switch(day) { case 1: case 2: case 3: case 4: case 5: printf("Weekday\n"); break; case 6: case 7: printf("Weekend\n"); break; default: printf("Invalid\n"); } includes default for invalid days, which is good practice.

4. Final Answer:

   Groups weekday cases 1-5 and weekend cases 6-7 with breaks and default -> Option B

5. Quick Check:

   Group cases with same output, add break after each group [OK]

Hint: Group cases with same output, add break after group [OK]

Common Mistakes:

• Printing wrong labels for grouped cases
• Missing breaks causing fall-through
• Not handling default case