If-else execution flow in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a number is positive.

C Sharp (C#)

int number = 5;
if (number [1] 0)
{
    Console.WriteLine("Positive number");
}

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 only if the number is zero.

The condition should check if the number is greater than zero to be positive.

2fill in blank

medium

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

C Sharp (C#)

int num = 4;
if (num % 2 [1] 0)
{
    Console.WriteLine("Even");
}

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 make sense for checking remainder.

The remainder when dividing by 2 is zero for even numbers.

3fill in blank

hard

Fix the error in the if-else statement to correctly print "Negative" or "Non-negative".

C Sharp (C#)

int val = -3;
if (val [1] 0)
{
    Console.WriteLine("Negative");
}
else
{
    Console.WriteLine("Non-negative");
}

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

A<=

B>=

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' will check for positive numbers instead.

Using '>=' or '<=' includes zero, which is not negative.

To print "Negative", the condition should check if val is less than zero.

4fill in blank

hard

Fill both blanks to print "Adult" if age is 18 or more, otherwise "Minor".

C Sharp (C#)

int age = 20;
if (age [1] 18)
{
    Console.WriteLine("Adult");
}
else
{
    Console.WriteLine("[2]");
}

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

A>=

B<

CMinor

DAdult

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' instead of '>=' reverses the logic.

Printing "Adult" in the else block is incorrect.

The condition checks if age is 18 or more (>= 18) to print "Adult"; otherwise, print "Minor".

5fill in blank

hard

Fill all three blanks to print "Fizz", "Buzz", or "FizzBuzz" based on divisibility.

C Sharp (C#)

int number = 15;
if (number [1] 3 == 0 && number [2] 5 == 0)
{
    Console.WriteLine("[3]");
}

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

A%

CFizzBuzz

DFizz

Attempts:

3 left

💡 Hint

Common Mistakes

Using '/' instead of '%' causes wrong checks.

Printing "Fizz" instead of "FizzBuzz" when divisible by both.

Use the modulus operator '%' to check divisibility. If divisible by both 3 and 5, print "FizzBuzz".

Practice

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

easy

A. Runs before the if block

B. Runs when the if condition is true

C. Runs only if there is no if block

D. Runs when the if condition is false

Solution

1. Step 1: Understand the if-else structure

   The if block runs when its condition is true.

2. Step 2: Role of the else block

   The else block runs only when the if condition is false.

3. Final Answer:

   Runs when the if condition is false -> Option D

4. Quick Check:

   else runs if if is false [OK]

Hint: Else runs only if if-condition is false [OK]

Common Mistakes:

• Thinking else runs when if is true
• Confusing else with else if
• Believing else runs before if

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

easy

A. if (condition) { } else { }

B. if condition { } else { }

C. if (condition) then { } else { }

D. if condition then { } else { }

Solution

1. Step 1: Check C# syntax rules

   C# requires parentheses around the condition in an if statement.

2. Step 2: Identify correct syntax

   Only if (condition) { } else { } uses parentheses and curly braces correctly.

3. Final Answer:

   if (condition) { } else { } -> Option A

4. Quick Check:

   Parentheses and braces required in C# if-else [OK]

Hint: Use parentheses around condition and braces for blocks [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using 'then' keyword incorrectly
• Missing curly braces

3. What is the output of this C# code?

int x = 5;
if (x > 10) {
    Console.WriteLine("Greater");
} else {
    Console.WriteLine("Smaller or equal");
}

medium

A. No output

B. Greater

C. Smaller or equal

D. Compilation error

Solution

1. Step 1: Evaluate the condition x > 10

   Since x is 5, 5 > 10 is false.

2. Step 2: Determine which block runs

   The else block runs because the if condition is false, printing "Smaller or equal".

3. Final Answer:

   Smaller or equal -> Option C

4. Quick Check:

   5 > 10 is false, so else runs [OK]

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

Common Mistakes:

• Assuming if block runs when condition is false
• Confusing output strings
• Thinking code has syntax errors

4. Identify the error in this C# code snippet:

int num = 7;
if num > 5 {
    Console.WriteLine("Big");
} else {
    Console.WriteLine("Small");
}

medium

A. Missing parentheses around condition

B. Missing semicolon after if statement

C. Missing curly braces around else block

D. Incorrect variable type

Solution

1. Step 1: Check if statement syntax

   C# requires parentheses around the condition in an if statement.

2. Step 2: Identify the error

   The code lacks parentheses around num > 5, causing a syntax error.

3. Final Answer:

   Missing parentheses around condition -> Option A

4. Quick Check:

   If condition must be in parentheses [OK]

Hint: Always put condition inside parentheses in if [OK]

Common Mistakes:

• Forgetting parentheses around condition
• Adding semicolon after if line
• Misplacing curly braces

5. You want to print "Positive", "Negative", or "Zero" based on an integer variable num. Which if-else structure correctly implements this?

hard

A. if (num > 0) { Console.WriteLine("Positive"); } else if (num <= 0) { Console.WriteLine("Negative"); } else { Console.WriteLine("Zero"); }

B. if (num > 0) { Console.WriteLine("Positive"); } else { if (num < 0) { Console.WriteLine("Negative"); } else { Console.WriteLine("Zero"); } }

C. if (num >= 0) { Console.WriteLine("Positive"); } else if (num <= 0) { Console.WriteLine("Negative"); } else { Console.WriteLine("Zero"); }

D. if (num > 0) { Console.WriteLine("Positive"); } else if (num > 0) { Console.WriteLine("Negative"); } else { Console.WriteLine("Zero"); }

Solution

1. Step 1: Understand the conditions needed

   We need to check if num is positive, negative, or zero.

2. Step 2: Analyze each option's logic

   if (num > 0) { Console.WriteLine("Positive"); } else { if (num < 0) { Console.WriteLine("Negative"); } else { Console.WriteLine("Zero"); } } correctly nests the else-if logic to handle all three cases without overlap or error.

3. Final Answer:

   if (num > 0) { Console.WriteLine("Positive"); } else { if (num < 0) { Console.WriteLine("Negative"); } else { Console.WriteLine("Zero"); } } -> Option B

4. Quick Check:

   Nested else-if covers all cases correctly [OK]

Hint: Use nested else if or else if for multiple conditions [OK]

Common Mistakes:

• Using overlapping conditions
• Missing zero case
• Repeating same condition twice