Use cases - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, World!" in C.

C

#include <stdio.h>

int main() {
    [1]("Hello, World!\n");
    return 0;
}

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

Aecho

Bprintf

Cprint

Dcout

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'print' instead of 'printf'.

Using 'echo' which is not a C function.

Using 'cout' which is from C++.

The printf function is used in C to print text to the console.

2fill in blank

medium

Complete the code to declare an integer variable named 'count' and assign it the value 10.

C

int [1] = 10;

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

Acount

Bnumber

Cvalue

Dtotal

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name than 'count'.

The variable name should be 'count' as specified.

3fill in blank

hard

Fix the error in the code to correctly compare if 'a' is greater than 'b'.

C

if (a [1] b) {
    printf("a is greater\n");
}

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

A>

B==

C=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which is assignment, not comparison.

Using '==' which checks equality, not greater than.

The '>' operator checks if 'a' is greater than 'b'.

4fill in blank

hard

Fill both blanks to create a for loop that counts from 0 to 4.

C

for (int i = [1]; i [2] 5; i++) {
    printf("%d\n", i);
}

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

A0

B<

C>

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 instead of 0.

Using 'i > 5' which would never run.

The loop starts at 0 and continues while i is less than 5.

5fill in blank

hard

Fill all three blanks to declare a function named 'add' that takes two integers and returns their sum.

C

int [1](int [2], int [3]) {
    return a + b;
}

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

Aadd

Ba

Cb

Dsum

Attempts:

3 left

💡 Hint

Common Mistakes

Using different parameter names than 'a' and 'b'.

Naming the function something other than 'add'.

The function name is 'add' and parameters are 'a' and 'b'.

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