Switch statement - Step-by-Step Execution

Concept Flow - Switch statement

Start

↓

Evaluate expression

↓

Match case?

No→Default case?

↓

Execute case

↓

Break?

No→Continue next case

Yes↓

Exit switch

The switch statement evaluates an expression, matches it to a case, executes that case's code, and exits or continues based on break statements.

Execution Sample

C

int x = 2;
switch (x) {
  case 1:
    printf("One\n");
    break;
  case 2:
    printf("Two\n");
    break;
  default:
    printf("Other\n");
}

This code checks the value of x and prints the matching case text.

Execution Table

Step	Expression Value	Case Checked	Match?	Action	Output
1	2	case 1	No	Skip case 1
2	2	case 2	Yes	Execute case 2 code	Two
3	2	break	N/A	Exit switch

💡 Break statement after case 2 causes exit from switch.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	2	2	2	2

Key Moments - 2 Insights

Why does the switch stop after printing "Two"?

Because of the break statement at step 3 in the execution_table, which exits the switch to prevent running other cases.

What happens if there is no break after a case?

The switch continues to execute the next case(s) until it finds a break or reaches the end, as shown by the 'Continue next case' path in the concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output at step 2?

A One

B Two

C Other

D No output

💡 Hint

Check the 'Output' column at step 2 in the execution_table.

At which step does the switch statement exit?

A Step 1

B Step 2

C Step 3

D It never exits

💡 Hint

Look at the 'Action' column and see when 'Exit switch' happens.

If the break at step 3 was removed, what would happen?

A Only case 2 runs

B Default case runs after case 2

C Program crashes

D No output at all

💡 Hint

Refer to the concept_flow where 'No break' leads to 'Continue next case'.

Concept Snapshot

switch(expression) {
  case value1:
    // code
    break;
  case value2:
    // code
    break;
  default:
    // code
}

- Evaluates expression once
- Matches cases in order
- Executes matching case
- break exits switch
- Without break, runs next cases

Full Transcript

The switch statement in C evaluates an expression and compares it to each case value. If a match is found, it executes that case's code. The break statement stops further case execution and exits the switch. Without break, execution continues to the next case. If no case matches, the default case runs if present. This example shows x=2 matching case 2, printing 'Two', then breaking to exit.

Practice

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

easy

A. To define a function

B. To repeat a block of code multiple times

C. To select one action from multiple choices based on a variable's value

D. To declare variables

Solution

1. Step 1: Understand the role of switch

   A switch statement chooses one path among many based on a variable's value.

2. Step 2: Compare with other options

   Loops repeat code, functions define reusable blocks, and declarations create variables, which are different from switch's purpose.

3. Final Answer:

   To select one action from multiple choices based on a variable's value -> Option C

4. Quick Check:

   Switch = Choice selection [OK]

Hint: Switch picks one case based on value, like a menu choice [OK]

Common Mistakes:

• Confusing switch with loops
• Thinking switch defines functions
• Believing switch declares variables

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

easy

A. switch (variable) { case 1: ... }

B. switch variable { case 1: ... }

C. switch [variable] { case 1: ... }

D. switch variable: case 1: ...

Solution

1. Step 1: Recall switch syntax

   The correct syntax uses parentheses around the variable: switch(variable) { ... }

2. Step 2: Check options

   Only switch (variable) { case 1: ... } uses parentheses correctly; others miss parentheses or use wrong brackets.

3. Final Answer:

   switch (variable) { case 1: ... } -> Option A

4. Quick Check:

   Switch needs parentheses around variable [OK]

Hint: Remember: switch(variable) uses parentheses, not brackets or none [OK]

Common Mistakes:

• Omitting parentheses around variable
• Using square brackets instead of parentheses
• Using colon instead of braces

3. What will be the output of this 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. No output

D. Two

Solution

1. Step 1: Identify the switch variable value

   The variable x is 2, so the switch checks case 2.

2. Step 2: Match case and output

   Case 2 matches, so it prints "Two" and then breaks to stop further checks.

3. Final Answer:

   Two -> Option D

4. Quick Check:

   Case 2 matches x=2, prints "Two" [OK]

Hint: Match variable value to case, print and break [OK]

Common Mistakes:

• Forgetting break causes fall-through
• Choosing default when case matches
• Confusing case numbers

4. Find 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

B. Missing default case

C. Wrong switch syntax

D. Variable n not declared

Solution

1. Step 1: Check each case for break

   Case 1 lacks a break, so if matched, it would fall through to case 2.

2. Step 2: Understand impact

   Missing break can cause unintended multiple prints; adding break after case 1 fixes this.

3. Final Answer:

   Missing break after case 1 -> Option A

4. Quick Check:

   Each case needs break to stop fall-through [OK]

Hint: Always add break after each case unless fall-through wanted [OK]

Common Mistakes:

• Ignoring missing break causes fall-through
• Thinking default is mandatory
• Assuming variable declaration error

5. You want to write a switch statement that prints "Weekend" for cases 6 and 7, and "Weekday" for cases 1 to 5. Which code correctly does this?

hard

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

B. 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"); }

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

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

Solution

1. Step 1: Group cases for same output

   Cases 1 to 5 print "Weekday", so group them before one printf and break.

2. Step 2: Group weekend cases

   Cases 6 and 7 print "Weekend" similarly grouped with break.

3. Step 3: Check default case

   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"); } includes default for invalid days, which is good practice.

4. Final Answer:

   Groups weekday cases 1-5 and weekend cases 6-7 with breaks and default -> Option B

5. Quick Check:

   Group cases with same output, add break after each group [OK]

Hint: Group cases with same output, add break after group [OK]

Common Mistakes:

• Printing wrong labels for grouped cases
• Missing breaks causing fall-through
• Not handling default case