Simple state machine with switch-case in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the state variable.

Embedded C

int state = [1];

Drag options to blanks, or click blank then click option'

A3

B1

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting the state from 1 instead of 0.

Using an uninitialized variable.

The initial state is usually set to 0 to start the state machine.

2fill in blank

medium

Complete the switch statement to check the current state.

Embedded C

switch([1]) {
    case 0:
        // do something
        break;
    case 1:
        // do something else
        break;
}

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Ainput

Bstate

Ccounter

Dflag

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable unrelated to the state machine in the switch.

Forgetting to put the variable inside the switch parentheses.

The switch statement should check the current state variable to decide the action.

3fill in blank

hard

Fix the error in the state update line.

Embedded C

case 0:
    // transition to state 1
    state [1] 1;
    break;

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A=

B=>

C!=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '=' for assignment.

Using invalid operators like '=>'.

Use the assignment operator '=' to update the state variable.

4fill in blank

hard

Fill both blanks to complete the state machine loop and switch.

Embedded C

while([1]) {
    switch([2]) {
        case 0:
            // do something
            state = 1;
            break;
        case 1:
            // do something else
            state = 0;
            break;
    }
}

Drag options to blanks, or click blank then click option'

A1

Bstate

C0

Drunning

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 in the while condition which stops the loop immediately.

Using a variable other than 'state' in the switch.

The loop runs while true (1), and the switch uses the state variable.

5fill in blank

hard

Fill all three blanks to add a default case and update the state machine.

Embedded C

switch(state) {
    case 0:
        // action for state 0
        state = [1];
        break;
    case 1:
        // action for state 1
        state = [2];
        break;
    default:
        // reset state
        state = [3];
        break;
}

Drag options to blanks, or click blank then click option'

A1

B0

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Setting wrong state transitions causing infinite loops.

Not handling the default case properly.

State 0 transitions to 1, state 1 transitions back to 0, and default resets to 0.

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