If–else statement in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is positive.

C

if (num [1] 0) {
    printf("Positive\n");
}

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

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' will check for negative numbers.

Using '==' checks for equality, not positivity.

The condition num > 0 checks if the number is positive.

2fill in blank

medium

Complete the code to print "Even" if the number is even.

C

if (num % 2 [1] 0) {
    printf("Even\n");
}

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

A>

B!=

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' will check for odd numbers instead.

Using '>' or '<' does not correctly check for evenness.

The condition num % 2 == 0 checks if the number is even.

3fill in blank

hard

Fix the error in the if statement to check if a number is negative.

C

if (num [1] 0) {
    printf("Negative\n");
}

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

A!=

B>

C==

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' checks for positive numbers instead.

Using '==' checks for zero, not negativity.

The condition num < 0 correctly checks if the number is negative.

4fill in blank

hard

Fill both blanks to complete the if-else statement that prints if a number is positive or not.

C

if (num [1] 0) {
    printf("Positive\n");
} else {
    printf("[2]\n");
}

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

A>

BNegative

CZero

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' in the first blank reverses the logic.

Printing 'Zero' instead of 'Negative' changes the meaning.

The condition num > 0 checks positivity, else it prints "Negative".

5fill in blank

hard

Fill all three blanks to complete the if-else if-else statement that checks if a number is positive, zero, or negative.

C

if (num [1] 0) {
    printf("Positive\n");
} else if (num [2] 0) {
    printf("Zero\n");
} else {
    printf("[3]\n");
}

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

A>

B==

CNegative

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up comparison operators.

Printing wrong labels for conditions.

The first condition checks if num > 0, second if num == 0, else prints "Negative".

Practice

1. What does an if-else statement do in C?

easy

A. It declares a variable.

B. It repeats a block of code multiple times.

C. It defines a new function.

D. It chooses between two actions based on a condition.

Solution

1. Step 1: Understand the purpose of if-else

   An if-else statement lets the program pick one of two paths depending on whether a condition is true or false.

2. Step 2: Match the description to the options

   Only It chooses between two actions based on a condition. describes choosing between two actions based on a condition, which is exactly what if-else does.

3. Final Answer:

   It chooses between two actions based on a condition. -> Option D

4. Quick Check:

   If-else = choose between two paths [OK]

Hint: If you want two choices, use if-else [OK]

Common Mistakes:

• Confusing if-else with loops
• Thinking if-else declares variables
• Mixing if-else with function definitions

2. Which of the following is the correct syntax for an if-else statement in C?

easy

A. if (condition) then { /* code */ } else { /* code */ }

B. if condition then { /* code */ } else { /* code */ }

C. if (condition) { /* code */ } else { /* code */ }

D. if condition { /* code */ } else { /* code */ }

Solution

1. Step 1: Recall C syntax rules for if-else

   In C, conditions must be inside parentheses and braces {} are used for code blocks.

2. Step 2: Check each option

   Only if (condition) { /* code */ } else { /* code */ } uses parentheses around the condition and braces correctly without extra keywords like 'then'.

3. Final Answer:

   if (condition) { /* code */ } else { /* code */ } -> Option C

4. Quick Check:

   Correct syntax uses parentheses and braces [OK]

Hint: Remember: if(condition) with braces {} [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using 'then' keyword (not in C)
• Skipping braces for multiple statements

3. What will be the output of this C code?

#include 
int main() {
    int x = 10;
    if (x > 5) {
        printf("Greater\n");
    } else {
        printf("Smaller\n");
    }
    return 0;
}

medium

A. Greater

B. Smaller

C. 10

D. No output

Solution

1. Step 1: Evaluate the condition x > 5

   Variable x is 10, which is greater than 5, so the condition is true.

2. Step 2: Determine which block runs

   Since the condition is true, the code inside the if block runs, printing "Greater".

3. Final Answer:

   Greater -> Option A

4. Quick Check:

   10 > 5 is true, so prints "Greater" [OK]

Hint: Check if condition is true or false to pick output [OK]

Common Mistakes:

• Confusing which block runs on true condition
• Ignoring the newline character in printf
• Assuming else block runs when condition is true

4. Find the error in this if-else code snippet:

int a = 3;
if a > 0
    printf("Positive\n");
else
    printf("Non-positive\n");

medium

A. Missing semicolon after if statement

B. Missing parentheses around condition in if statement

C. Missing braces around printf statements

D. Incorrect else keyword

Solution

1. Step 1: Check syntax of if condition

   In C, the condition in an if statement must be inside parentheses (). Here, it is missing.

2. Step 2: Verify other parts

   Semicolons after printf are present, braces are optional for single statements, and else keyword is correct.

3. Final Answer:

   Missing parentheses around condition in if statement -> Option B

4. Quick Check:

   if condition needs parentheses ( ) [OK]

Hint: Always put condition inside parentheses ( ) [OK]

Common Mistakes:

• Forgetting parentheses in if condition
• Thinking braces are always required for single statements
• Misplacing else keyword

5. You want to write a program that prints "Even" if a number is even, and "Odd" if it is odd. Which if-else code correctly does this in C?

hard

A. if (num % 2 == 0) { printf("Even\n"); } else { printf("Odd\n"); }

B. if (num / 2 == 0) { printf("Even\n"); } else { printf("Odd\n"); }

C. if (num % 2 = 0) { printf("Even\n"); } else { printf("Odd\n"); }

D. if (num % 2 != 0) { printf("Even\n"); } else { printf("Odd\n"); }

Solution

1. Step 1: Understand how to check even numbers

   A number is even if dividing by 2 leaves remainder 0, which is checked by num % 2 == 0.

2. Step 2: Analyze each option

   if (num % 2 == 0) { printf("Even\n"); } else { printf("Odd\n"); } correctly uses modulus operator and equality check. if (num / 2 == 0) { printf("Even\n"); } else { printf("Odd\n"); } uses division instead of modulus. if (num % 2 = 0) { printf("Even\n"); } else { printf("Odd\n"); } uses assignment (=) instead of comparison (==). if (num % 2 != 0) { printf("Even\n"); } else { printf("Odd\n"); } reverses the logic.

3. Final Answer:

   if (num % 2 == 0) { printf("Even\n"); } else { printf("Odd\n"); } -> Option A

4. Quick Check:

   Use modulus == 0 to check even [OK]

Hint: Use num % 2 == 0 to test even numbers [OK]

Common Mistakes:

• Using division instead of modulus
• Using = instead of == in condition
• Reversing even and odd logic