Use cases - Deep Dive

Overview - Use cases

What is it?

Use cases describe how a program or system is used to achieve specific goals. They show the steps a user or another system takes to interact with the program. In C programming, use cases help plan what the program should do before writing code. They guide developers to build features that solve real problems.

Why it matters

Without use cases, programmers might write code that doesn't meet user needs or misses important steps. Use cases ensure the program solves the right problems and works as expected. They save time and effort by clarifying requirements early. This leads to better software that users find helpful and easy to use.

Where it fits

Before learning use cases, you should understand basic programming concepts like variables, functions, and control flow. After mastering use cases, you can learn about software design patterns and testing, which build on clear requirements. Use cases fit in the planning and design phase of software development.

Mental Model

Core Idea

Use cases are stories that describe how users interact with a program to achieve a goal.

Think of it like...

Use cases are like a recipe that tells you step-by-step how to make a dish, ensuring you get the right result every time.

┌───────────────┐
│   User Goal   │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Use Case Steps│
│ 1. Start      │
│ 2. Action     │
│ 3. Result     │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Program Output│
└───────────────┘

Build-Up - 7 Steps

1

Foundation

What is a Use Case?

Concept: Introduce the idea of use cases as simple stories describing user interactions.

A use case explains how someone uses a program to do something. For example, a use case for a calculator program might be 'Add two numbers.' It shows the steps the user takes and what the program does in response.

Result

You understand that use cases describe user goals and program responses in simple steps.

Understanding use cases helps you think about programs from the user's point of view, not just code.

2

Foundation

Basic Structure of Use Cases

Concept: Learn the parts that make up a use case: actors, goals, and steps.

Use cases have actors (users or systems), goals (what they want to do), and steps (actions taken). For example, in a login use case, the actor is the user, the goal is to access their account, and steps include entering username and password.

Result

You can identify the main parts of a use case and explain them clearly.

Knowing the structure helps you write clear and complete use cases that guide programming.

3

Intermediate

Writing Use Cases for C Programs

🤔Before reading on: do you think use cases are only for big programs or also useful for small C programs? Commit to your answer.

Concept: Use cases apply to all program sizes and help plan C programs by describing user interactions.

Even small C programs benefit from use cases. For example, a program that reads numbers and finds the largest can have a use case: 'User inputs numbers, program outputs the largest.' Writing this helps clarify what the program must do before coding.

Result

You can write simple use cases for C programs to plan their behavior.

Using use cases early prevents confusion and errors during coding, even in small projects.

4

Intermediate

Use Cases and Function Design

🤔Before reading on: do you think use cases directly influence how you write functions in C? Commit to your answer.

Concept: Use cases guide how to break down program tasks into functions in C.

Each step in a use case can become a function or part of a function. For example, a use case for a calculator might have steps like 'get input,' 'calculate result,' and 'display output.' In C, you can write separate functions for each step to keep code organized.

Result

You understand how use cases help design clear, modular functions.

Connecting use cases to functions improves code clarity and makes programs easier to maintain.

5

Intermediate

Handling Alternative Paths in Use Cases

🤔Before reading on: do you think use cases only describe the main success path or also errors and exceptions? Commit to your answer.

Concept: Use cases include alternative paths for errors or different choices users might make.

A use case might say: 'If the user enters invalid input, show an error message and ask again.' This helps programmers plan how to handle mistakes. In C, this means adding checks and loops to manage these cases.

Result

You can write use cases that cover both normal and error scenarios.

Including alternative paths in use cases leads to more robust and user-friendly programs.

6

Advanced

Use Cases in Large C Projects

🤔Before reading on: do you think use cases help coordinate teams in big C projects? Commit to your answer.

Concept: Use cases serve as a communication tool among team members in large projects.

In big projects, many programmers work on different parts. Use cases describe what the whole program should do, so everyone understands the goals. They help divide work and check that all parts fit together. For example, a use case for a file manager program might involve opening, reading, and saving files, each handled by different team members.

Result

You see how use cases improve teamwork and project planning.

Using use cases prevents misunderstandings and duplicated work in teams.

7

Expert

Limitations and Evolution of Use Cases

🤔Before reading on: do you think use cases alone are enough to fully specify complex C programs? Commit to your answer.

Concept: Use cases are powerful but have limits; they often need to be combined with other design tools.

Use cases describe what happens but not how. For complex C programs, you also need detailed designs like flowcharts, data structures, and algorithms. Use cases evolve as requirements change, so they must be updated to keep the program aligned with user needs.

Result

You understand the role and limits of use cases in software design.

Knowing when to complement use cases with other tools leads to better software design and fewer bugs.

Under the Hood

Use cases work by capturing user goals and interactions as sequences of steps. These steps translate into program requirements and guide code structure. Internally, they help define inputs, outputs, and decision points that the program must handle. This creates a clear map from user needs to program behavior.

Why designed this way?

Use cases were created to bridge the gap between users and programmers. Before use cases, programmers often misunderstood what users wanted, leading to wasted effort. Use cases provide a simple, story-like format that anyone can understand, making communication easier and reducing errors.

┌───────────────┐
│   User/Actor  │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Use Case Steps│
│ - Input      │
│ - Process    │
│ - Output     │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│   C Program   │
│ - Functions  │
│ - Logic      │
└───────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Do use cases only describe what the program does, not how it does it? Commit yes or no.

Common Belief: Use cases tell programmers exactly how to write the code step-by-step.

Reality: Use cases describe what the program should do, not the internal code details or algorithms.

Why it matters: Confusing use cases with code design can lead to rigid programs and missed opportunities for better solutions.

Quick: Are use cases only useful for big, complex programs? Commit yes or no.

Common Belief: Use cases are only needed for large software projects.

Reality: Use cases help plan programs of all sizes, even small C programs benefit from clear use cases.

Why it matters: Ignoring use cases in small projects can cause confusion and bugs that are easy to avoid.

Quick: Do use cases replace the need for testing? Commit yes or no.

Common Belief: Once use cases are written, testing is not necessary.

Reality: Use cases guide testing but do not replace it; testing verifies the program works as intended.

Why it matters: Skipping testing leads to programs that may meet use cases on paper but fail in real use.

Quick: Do use cases always stay the same throughout a project? Commit yes or no.

Common Belief: Use cases are fixed and do not change once written.

Reality: Use cases evolve as user needs and requirements change during development.

Why it matters: Treating use cases as fixed can cause the program to become outdated or miss new features.

Expert Zone

1

Use cases often omit low-level details, so experienced developers must infer or design the internal logic carefully.

2

In large projects, use cases can overlap or conflict; managing them requires skill and clear documentation.

3

Use cases can be linked to test cases, creating a traceable path from requirements to verification.

When NOT to use

Use cases are less effective for programs that are purely algorithmic with no user interaction, such as background services or embedded systems. In such cases, formal specifications or state machines may be better.

Production Patterns

In professional C projects, use cases are often part of requirements documents reviewed by teams. They guide modular design, help create user manuals, and serve as a basis for automated testing scripts.

Connections

User Stories (Agile Development)

Builds-on

Use cases and user stories both describe user needs, but user stories are shorter and more flexible, helping teams adapt quickly.

Finite State Machines

Complementary

Use cases describe user goals and steps, while finite state machines model program states and transitions, together providing a full picture of behavior.

Instruction Manuals (Technical Writing)

Similar pattern

Both use cases and instruction manuals guide users through steps to achieve goals, showing how clear communication improves usability.

Common Pitfalls

#1 Writing use cases that are too vague or general.

Wrong approach:

Use Case: 'User uses the program to do tasks.'

Correct approach:

Use Case: 'User inputs two numbers, program calculates and displays their sum.'

Root cause:

Not focusing on specific user goals and steps leads to unclear requirements.

#2 Ignoring alternative or error paths in use cases.

Wrong approach:

Use Case: 'User enters valid input and program shows result.'

Correct approach:

Use Case: 'If user enters invalid input, program shows error and asks again.'

Root cause:

Assuming everything always goes right causes programs to fail in real situations.

#3 Treating use cases as detailed code instructions.

Wrong approach:

Use Case: 'Call function A, then function B, then print output.'

Correct approach:

Use Case: 'User requests data processing, program performs calculations and shows results.'

Root cause:

Confusing what the program does with how it does it limits design flexibility.

Key Takeaways

Use cases describe how users interact with programs to achieve specific goals in clear, simple steps.

They help programmers understand what to build before writing code, improving communication and reducing errors.

Use cases include normal and alternative paths, making programs more robust and user-friendly.

They are useful for all program sizes and help teams coordinate work in large projects.

Use cases guide design but do not replace detailed coding or testing; they evolve as requirements change.