Else-if ladder execution in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the number is positive.

C Sharp (C#)

int number = 10;
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 number equals zero, not positive.

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

2fill in blank

medium

Complete the else-if condition to check if the number is zero.

C Sharp (C#)

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

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

A!=

B>

C<

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' will check for any number except zero.

Using '<' or '>' will check for negative or positive numbers, not zero.

The condition number == 0 checks if the number is exactly zero.

3fill in blank

hard

Fix the error in the else-if ladder to correctly check if the number is negative.

C Sharp (C#)

int number = -5;
if (number > 0)
{
    Console.WriteLine("Positive number");
}
else if (number == 0)
{
    Console.WriteLine("Zero");
}
else if (number [1] 0)
{
    Console.WriteLine("Negative number");
}

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, not negative.

Using '==' checks for equality, not less than.

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

4fill in blank

hard

Fill both blanks to complete the else-if ladder that prints the correct message based on the number.

C Sharp (C#)

int number = 0;
if (number [1] 0)
{
    Console.WriteLine("Positive number");
}
else if (number [2] 0)
{
    Console.WriteLine("Negative number");
}

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

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' in these conditions will not separate positive and negative numbers.

Swapping the operators will cause wrong messages.

The first condition checks if number is greater than zero (positive), the second checks if less than zero (negative).

5fill in blank

hard

Fill all three blanks to complete the else-if ladder that prints the correct message for positive, zero, or negative numbers.

C Sharp (C#)

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

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

A>

B==

CNegative

DZero

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong operators in conditions.

Printing wrong message in else block.

The first condition checks if number is greater than zero (positive). The second checks if number equals zero. The else prints "Negative number" for all other cases.

Practice

1. What happens in an else-if ladder when the first condition is true?

easy

A. All conditions are checked and all true blocks run.

B. The program skips all conditions and runs the else block.

C. Only the code inside that first true condition runs.

D. The program throws an error.

Solution

1. Step 1: Understand else-if ladder behavior

   In an else-if ladder, conditions are checked one by one from top to bottom.

2. Step 2: Identify what happens when a condition is true

   When the first true condition is found, its code block runs and the rest are skipped.

3. Final Answer:

   Only the code inside that first true condition runs. -> Option C

4. Quick Check:

   First true condition runs only [OK]

Hint: First true condition runs, others skipped [OK]

Common Mistakes:

• Thinking all true conditions run
• Believing else block runs even if a condition is true
• Assuming conditions run in parallel

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

easy

A. if condition { } else if (condition) { } else { }

B. if (condition) { } elseif (condition) { } else { }

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

D. if (condition) { } else if (condition) { } else { }

Solution

1. Step 1: Recall correct else-if syntax in C#

   The correct keyword is else if with a space, and conditions must be in parentheses.

2. Step 2: Check each option for syntax errors

   if (condition) { } else if (condition) { } else { } uses correct if (condition), then else if (condition), and finally else. Others have syntax errors like missing parentheses or wrong keyword.

3. Final Answer:

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

4. Quick Check:

   Correct else-if syntax = if (condition) { } else if (condition) { } else { } [OK]

Hint: Use 'else if' with parentheses for conditions [OK]

Common Mistakes:

• Writing 'elseif' as one word
• Omitting parentheses around conditions
• Using 'if' without parentheses

3. What is the output of this code?

int x = 15;
if (x < 10)
  Console.WriteLine("Less than 10");
else if (x < 20)
  Console.WriteLine("Less than 20");
else
  Console.WriteLine("20 or more");

medium

A. Less than 10

B. Less than 20

C. 20 or more

D. No output

Solution

1. Step 1: Evaluate first condition (x < 10)

   x is 15, which is not less than 10, so this condition is false.

2. Step 2: Evaluate second condition (x < 20)

   15 is less than 20, so this condition is true and its block runs.

3. Final Answer:

   Less than 20 -> Option B

4. Quick Check:

   15 < 20 is true, so prints 'Less than 20' [OK]

Hint: Check conditions top-down; first true runs [OK]

Common Mistakes:

• Choosing 'Less than 10' because 15 is close
• Ignoring else-if and picking else block
• Thinking no output if first false

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

int score = 85;
if score >= 90
  Console.WriteLine("Grade A");
else if (score >= 80)
  Console.WriteLine("Grade B");
else
  Console.WriteLine("Grade C");

medium

A. Missing parentheses around first if condition

B. Missing semicolon after Console.WriteLine

C. Incorrect else-if keyword

D. No error

Solution

1. Step 1: Check syntax of first if statement

   The first if condition is written as if score >= 90 without parentheses, which is invalid in C#.

2. Step 2: Verify other parts

   Other conditions have correct parentheses and syntax. The semicolons are correctly placed after each Console.WriteLine statement.

3. Final Answer:

   Missing parentheses around first if condition -> Option A

4. Quick Check:

   if conditions need parentheses [OK]

Hint: Always put conditions inside parentheses [OK]

Common Mistakes:

• Omitting parentheses in if condition
• Confusing semicolon necessity after method calls
• Miswriting else-if keyword

5. You want to categorize an integer n as 'Negative', 'Zero', or 'Positive' using an else-if ladder. Which code correctly implements this?

hard

A. if (n < 0) Console.WriteLine("Negative"); else if (n == 0) Console.WriteLine("Zero"); else Console.WriteLine("Positive");

B. if (n >= 0) Console.WriteLine("Positive"); else if (n == 0) Console.WriteLine("Zero"); else Console.WriteLine("Negative");

C. if n > 0 Console.WriteLine("Positive"); else if (n == 0) Console.WriteLine("Zero"); else Console.WriteLine("Negative");

D. if (n == 0) Console.WriteLine("Zero"); else if n > 0 Console.WriteLine("Positive"); else Console.WriteLine("Negative");

Solution

1. Step 1: Understand the categories and conditions

   We want to print 'Negative' if n < 0, 'Zero' if n == 0, and 'Positive' if n > 0.

2. Step 2: Check each option for correct condition order and logic

   if (n < 0) Console.WriteLine("Negative"); else if (n == 0) Console.WriteLine("Zero"); else Console.WriteLine("Positive"); checks n < 0 first, then n == 0, else prints 'Positive'. This covers all cases correctly.

3. Final Answer:

   if (n < 0) Console.WriteLine("Negative"); else if (n == 0) Console.WriteLine("Zero"); else Console.WriteLine("Positive"); -> Option A

4. Quick Check:

   Correct order and conditions for categories [OK]

Hint: Check negative first, zero second, else positive [OK]

Common Mistakes:

• Checking positive before zero causing wrong output
• Using >= 0 for positive including zero
• Misordering conditions causing unreachable code