Use cases - Mini Project: Build & Apply

Use Cases in C Programming

📖 Scenario: You are building a simple program to decide what message to show based on a user's role in a system.

🎯 Goal: Create a C program that uses switch statements to print different messages for different user roles.

📋 What You'll Learn

Create an integer variable called role with a specific value

Create a switch statement using the variable role

Handle cases for roles 1, 2, and 3 with different messages

Include a default case for unknown roles

Print the message corresponding to the role

💡 Why This Matters

🌍 Real World

Switch statements are used in programs to make decisions based on different conditions, like user roles, menu choices, or error codes.

💼 Career

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

1

Create the role variable

Create an integer variable called role and set it to 2.

C

# Create an integer variable called role and set it to 2
// Your code here

Hint

Use int role = 2; inside the main function.

2

Add the switch statement

Add a switch statement using the variable role inside the main function.

C

#include 

int main() {
    int role = 2;
    // Add a switch statement using role
    // Your code here
    return 0;
}

Hint

Write switch(role) { } inside main.

3

Add cases for roles 1, 2, and 3

Inside the switch(role), add cases for 1, 2, and 3. For each case, add a printf statement with these exact messages:
"Admin access granted\n" for case 1,
"User access granted\n" for case 2,
"Guest access granted\n" for case 3.
Don't forget to add break; after each printf.

C

#include 

int main() {
    int role = 2;
    switch(role) {
        // Add cases 1, 2, 3 with printf and break
        // Your code here
    }
    return 0;
}

Hint

Use case 1:, case 2:, case 3: with printf and break;.

4

Add a default case and print the message

Add a default case inside the switch(role) that prints "Unknown role\n". Then, add a printf statement to print the message for the current role when the program runs.

C

#include 

int main() {
    int role = 2;
    switch(role) {
        case 1:
            printf("Admin access granted\n");
            break;
        case 2:
            printf("User access granted\n");
            break;
        case 3:
            printf("Guest access granted\n");
            break;
        // Add default case here
        // Your code here
    }
    return 0;
}

Hint

Use default: with printf("Unknown role\n"); and break;.

Practice

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

easy

A. To declare variables

B. To choose between multiple actions based on the value of a variable

C. To define a function

D. To repeat a block of code multiple times

Solution

1. Step 1: Understand the role of switch

   The switch statement is used to select one of many code blocks to execute based on a variable's value.

2. Step 2: Compare with other options

   Declaring variables, repeating a block of code multiple times, and defining a function are not the purpose of switch.

3. Final Answer:

   To choose between multiple actions based on the value of a variable -> Option B

4. Quick Check:

   switch selects code by value [OK]

Hint: Switch picks code based on variable value, like a menu choice [OK]

Common Mistakes:

• Confusing switch with loops
• Thinking switch declares variables
• Using switch to define functions

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

easy

A. switch(variable) {

B. switch variable {

C. switch variable() {

D. switch { variable }

Solution

1. Step 1: Recall correct switch syntax

   The correct syntax requires the keyword switch followed by parentheses enclosing the variable, then an opening brace.

2. Step 2: Check each option

   switch(variable) { matches the correct syntax: switch(variable) {. Others miss parentheses or use wrong braces.

3. Final Answer:

   switch(variable) { -> Option A

4. Quick Check:

   Syntax needs parentheses around variable [OK]

Hint: Remember: switch(variable) with parentheses and braces [OK]

Common Mistakes:

• Omitting parentheses around variable
• Using wrong braces or brackets
• Adding parentheses after variable name

3. What will be the output of the following 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. Two

D. No output

Solution

1. Step 1: Identify the value of variable x

   The variable x is set to 2.

2. Step 2: Match x with case labels

   The switch checks cases: 1 and 2. Since x is 2, it matches case 2 and prints "Two".

3. Final Answer:

   Two -> Option C

4. Quick Check:

   Value 2 matches case 2 [OK]

Hint: Match variable value to case label to find output [OK]

Common Mistakes:

• Ignoring break and falling through
• Choosing default when case matches
• Confusing case numbers

4. Identify 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 causes fall-through

B. Variable n is not declared

C. Default case must be first

D. Switch cannot use integers

Solution

1. Step 1: Check for break statements

   Case 1 lacks a break, so after printing "One", execution continues to case 2.

2. Step 2: Understand consequences of missing break

   This fall-through causes both "One" and "Two" to print when n is 1, which is usually unintended.

3. Final Answer:

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

4. Quick Check:

   Always add break to prevent fall-through [OK]

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

Common Mistakes:

• Forgetting break after cases
• Thinking default must be first
• Believing switch can't use integers

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

hard

A. switch(day) {
if(day >= 1 && day <= 5) {
printf("Weekday\n");
} else if(day == 6 || day == 7) {
printf("Weekend\n");
} else {
printf("Invalid\n");
}
}

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

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

D. 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");
}

Solution

1. Step 1: Understand valid switch syntax for multiple cases

   Cases can be grouped by listing them one after another without breaks to share code.

2. Step 2: Evaluate each option

   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"); } correctly groups cases 1 to 5 and 6 to 7, with breaks and a default. switch(day) { case 1: printf("Weekday\n"); case 2: printf("Weekday\n"); case 3: printf("Weekday\n"); case 4: printf("Weekday\n"); case 5: printf("Weekday\n"); case 6: printf("Weekend\n"); case 7: printf("Weekend\n"); default: printf("Invalid\n"); } lacks breaks causing fall-through. switch(day) { case 1 ... 5: printf("Weekday\n"); break; case 6 ... 7: printf("Weekend\n"); break; default: printf("Invalid\n"); } uses invalid syntax (case 1 ... 5). switch(day) { if(day >= 1 && day <= 5) { printf("Weekday\n"); } else if(day == 6 || day == 7) { printf("Weekend\n"); } else { printf("Invalid\n"); } } uses if inside switch without case labels, making the body unreachable and invalid for switch logic.

3. Final Answer:

   Groups cases by listing consecutive cases for shared execution with breaks -> Option D

4. Quick Check:

   Group cases by listing them, add breaks [OK]

Hint: Group cases by listing them; use breaks to separate [OK]

Common Mistakes:

• Using invalid range syntax in case
• Missing breaks causing fall-through
• Trying to use if inside switch