Simple state machine with switch-case in Embedded C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a state machine in programming?

A state machine is a way to organize code where the program can be in one state at a time and changes states based on events or conditions.

beginner

How does the switch-case statement help in implementing a state machine?

Switch-case lets you check the current state and run different code for each state clearly and simply.

beginner

In a simple state machine, what does each case in the switch represent?

Each case represents one possible state of the machine and contains the code to run when in that state.

intermediate

Why is it important to have a default case in a switch statement for a state machine?

The default case handles unexpected states, helping to catch errors or reset the machine safely.

beginner

What is the role of a state variable in a simple state machine?

The state variable keeps track of the current state so the program knows what to do next.

What does each 'case' in a switch statement represent in a state machine?

A An error handler

B A function call

C A variable declaration

D A possible state of the machine

Each case corresponds to one state in the state machine.

Why use a switch-case instead of many if-else statements for states?

A If-else cannot handle states

B Switch-case runs faster than if-else always

C Switch-case is clearer and easier to read for multiple states

D Switch-case uses less memory

Switch-case organizes multiple states clearly, improving readability.

What should you do if the state variable has an unexpected value?

A Ignore it

B Handle it in the default case

C Restart the program

D Use a loop

The default case catches unexpected states to handle errors safely.

What type of variable usually holds the current state in embedded C?

A An enum or integer

B A float

C A string

D A pointer

States are often represented by enums or integers for efficiency.

What happens inside each case of the switch in a state machine?

A Code runs to perform actions and possibly change the state

B The program ends

C Variables are declared only

D Nothing happens

Each case runs code for that state and may update the state variable.

Explain how a simple state machine works using a switch-case statement in embedded C.

Think about how the program decides what to do based on the current state.

Describe why using a switch-case is a good choice for implementing a simple state machine.

Consider how switch-case helps keep code clean and easy to follow.

Practice

1.

What is the main purpose of using a switch-case statement in a simple state machine?

easy

A. To create loops that repeat forever

B. To handle different states clearly and execute code based on the current state

C. To declare variables for each state

D. To stop the program immediately

Solution

1. Step 1: Understand the role of switch-case in state machines

   The switch-case statement lets the program choose what to do based on the current state value.

2. Step 2: Recognize how states are handled

   Each case corresponds to a state, so the program runs code specific to that state.

3. Final Answer:

   To handle different states clearly and execute code based on the current state -> Option B

4. Quick Check:

   switch-case manages states = To handle different states clearly and execute code based on the current state [OK]

Hint: Switch-case matches states to actions clearly [OK]

Common Mistakes:

• Thinking switch-case creates loops
• Confusing variable declaration with state handling
• Assuming switch-case stops the program

2.

Which of the following is the correct syntax for a switch statement in embedded C?

switch(state) {
  case 0:
    // code
    break;
  case 1:
    // code
    break;
  default:
    // code
}

easy

A. switch state { case 0: ... break; case 1: ... break; default: ... }

B. switch(state) { case 0: ... case 1: ... default: ... }

C. switch(state) case 0: ... break; case 1: ... break; default: ...

D. switch(state) { case 0: ... break; case 1: ... break; default: ... }

Solution

1. Step 1: Check the syntax structure of switch-case

   The switch statement requires parentheses around the variable and braces around the cases.

2. Step 2: Verify the use of colons and breaks

   Each case must have a colon and usually ends with a break to prevent fall-through.

3. Final Answer:

   switch(state) { case 0: ... break; case 1: ... break; default: ... } -> Option D

4. Quick Check:

   Correct switch-case syntax = switch(state) { case 0: ... break; case 1: ... break; default: ... } [OK]

Hint: Remember switch needs parentheses and braces [OK]

Common Mistakes:

• Omitting parentheses after switch
• Missing colons after case labels
• Forgetting break statements

3.

What will be the output of this code snippet?

int state = 1;
switch(state) {
  case 0:
    printf("State is zero\n");
    break;
  case 1:
    printf("State is one\n");
    break;
  default:
    printf("Unknown state\n");
}

medium

A. Unknown state

B. State is zero

C. State is one

D. No output

Solution

1. Step 1: Identify the value of state

   The variable state is set to 1 before the switch statement.

2. Step 2: Match the case with state value

   The switch matches case 1, so it prints "State is one" and then breaks.

3. Final Answer:

   State is one -> Option C

4. Quick Check:

   state=1 prints "State is one" [OK]

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

Common Mistakes:

• Confusing case 0 with case 1
• Forgetting break causes fall-through
• Assuming default runs when case matches

4.

Find the error in this state machine code snippet:

int state = 0;
switch(state) {
  case 0:
    printf("Start\n");
  case 1:
    printf("Running\n");
    break;
  default:
    printf("Unknown\n");
}

medium

A. Missing break after case 0 causes fall-through

B. Switch statement missing parentheses

C. Default case should be first

D. Variable state is not initialized

Solution

1. Step 1: Check each case for break statements

   Case 0 does not have a break, so after printing "Start", it continues to case 1.

2. Step 2: Understand fall-through effect

   This causes both "Start" and "Running" to print when state is 0, which may be unintended.

3. Final Answer:

   Missing break after case 0 causes fall-through -> Option A

4. Quick Check:

   Missing break causes fall-through = Missing break after case 0 causes fall-through [OK]

Hint: Always add break after each case to avoid fall-through [OK]

Common Mistakes:

• Ignoring missing break leads to unexpected output
• Thinking default must be first case
• Assuming uninitialized variable error

5.

You want to design a simple state machine with three states: INIT (0), PROCESS (1), and DONE (2). The machine should start at INIT, then move to PROCESS, and finally to DONE. Which code snippet correctly updates the state inside the switch-case?

int state = 0;
switch(state) {
  case 0:
    // Move to PROCESS
    state = 1;
    break;
  case 1:
    // Move to DONE
    state = 2;
    break;
  case 2:
    // Finished
    break;
}

hard

A. Correctly updates state from INIT to PROCESS to DONE

B. Does not update state, stays in INIT forever

C. Skips PROCESS and goes directly to DONE

D. Causes infinite loop without state change

Solution

1. Step 1: Check state transitions in each case

   Case 0 sets state to 1 (PROCESS), case 1 sets state to 2 (DONE), case 2 does nothing (finished).

2. Step 2: Confirm the order of states

   The code moves from INIT to PROCESS to DONE in order, updating the state variable correctly.

3. Final Answer:

   Correctly updates state from INIT to PROCESS to DONE -> Option A

4. Quick Check:

   State updates follow sequence = Correctly updates state from INIT to PROCESS to DONE [OK]

Hint: Update state variable inside each case to move forward [OK]

Common Mistakes:

• Not updating state variable inside cases
• Skipping intermediate states
• Forgetting break causing unexpected behavior