Use cases - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a use case in programming?

A use case describes how a user or system interacts with a program to achieve a goal. It shows the steps and actions needed.

beginner

Why are use cases important before coding?

Use cases help understand what the program should do. They guide developers to write code that meets user needs.

beginner

Give an example of a simple use case for a calculator program.

Example: User wants to add two numbers. Steps: 1) User enters first number. 2) User enters second number. 3) User presses '+' button. 4) Program shows the sum.

intermediate

How do use cases help in testing a program?

Use cases provide scenarios to check if the program works as expected. Testers follow use case steps to find errors.

intermediate

What is the difference between a use case and a function in C?

A use case is about what the program should do from a user's view. A function is a block of code that performs a specific task inside the program.

What does a use case describe?

A The speed of program execution

B The syntax rules of the C language

C How users interact with a program to achieve a goal

D The memory layout of a program

A use case shows the interaction between users and the program to reach a goal.

Which is NOT a benefit of writing use cases before coding?

A Automatically generates code

B Guides program design

C Helps understand user needs

D Supports testing

Use cases help plan and test but do not automatically create code.

In a use case, what is the main focus?

A Variable declarations

B Hardware specifications

C Compiler errors

D User actions and program responses

Use cases focus on what users do and how the program responds.

How can use cases help testers?

A By fixing bugs automatically

B By providing scenarios to check program behavior

C By writing new functions

D By compiling the program

Testers use use cases as guides to verify the program works correctly.

Which statement is true about use cases and functions?

A Use cases describe user goals; functions are code blocks

B Functions describe user goals; use cases are code blocks

C Use cases and functions are the same

D Functions are only used in testing

Use cases explain what users want; functions are parts of the program code.

Explain what a use case is and why it is useful before writing C code.

Think about how use cases help plan what the program should do.

Describe how use cases can assist in testing a C program.

Consider how testers use step-by-step actions to verify the program.

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