Constant patterns in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the variable value equals 10 using a constant pattern.

C Sharp (C#)

if (value is [1]) {
    Console.WriteLine("Value is 10");
}

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

A"10"

B10

Cvalue

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the number, which makes it a string.

Using the variable name instead of a constant.

Using a boolean value instead of a constant.

The constant pattern checks if the variable matches the constant value 10.

2fill in blank

medium

Complete the code to print a message when input equals the character 'A' using a constant pattern.

C Sharp (C#)

if (input is [1]) {
    Console.WriteLine("Input is A");
}

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

A'A'

B"A"

CA

D'a'

Attempts:

3 left

💡 Hint

Common Mistakes

Using double quotes which makes it a string.

Using uppercase without quotes.

Using lowercase character instead of uppercase.

The constant pattern for a character uses single quotes around the character.

3fill in blank

hard

Fix the error in the code to correctly check if status equals the boolean constant true using a constant pattern.

C Sharp (C#)

if (status is [1]) {
    Console.WriteLine("Status is true");
}

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

A"true"

BTrue

Ctrue

DTRUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase True or TRUE which are invalid.

Using quotes which makes it a string.

Using incorrect casing.

The boolean constant true is lowercase in C# and used directly in the pattern.

4fill in blank

hard

Fill both blanks to check if number is either 0 or 1 using constant patterns in a switch expression.

C Sharp (C#)

string result = number switch {
    [1] => "Zero",
    [2] => "One",
    _ => "Other"
};

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

A0

B1

C"0"

D"1"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string constants instead of numeric constants.

Mixing quotes and no quotes incorrectly.

Using wrong numbers.

Use numeric constants 0 and 1 without quotes for constant patterns in switch expressions.

5fill in blank

hard

Fill all three blanks to create a switch expression that returns a message for grade being 'A', 'B', or any other character using constant patterns.

C Sharp (C#)

string message = grade switch {
    [1] => "Excellent",
    [2] => "Good",
    [3] => "Needs Improvement"
};

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

A'A'

B'B'

C_

D'C'

Attempts:

3 left

💡 Hint

Common Mistakes

Using double quotes for characters.

Not using the discard pattern for the default case.

Using wrong characters.

Use character constants with single quotes for 'A' and 'B', and the discard pattern '_' for any other value.

Practice

1. What does a constant pattern in C# do when used in a switch statement?

easy

A. It checks if the value is greater than a constant.

B. It checks if the value exactly matches a fixed constant.

C. It checks if the value is less than a constant.

D. It checks if the value is of a certain type.

Solution

1. Step 1: Understand constant pattern purpose

   Constant patterns compare a value to a fixed constant to see if they are equal.

2. Step 2: Apply to switch statement

   In a switch, constant patterns match cases where the value equals the constant exactly.

3. Final Answer:

   It checks if the value exactly matches a fixed constant. -> Option B

4. Quick Check:

   Constant pattern = exact value check [OK]

Hint: Constant pattern means exact value match check [OK]

Common Mistakes:

• Thinking it checks ranges instead of exact values
• Confusing with type patterns
• Assuming it checks inequality

2. Which of the following is the correct syntax for a constant pattern in an if statement in C#?

easy

A. if (is x 10) { }

B. if (x == is 10) { }

C. if (x is 10) { }

D. if (x = 10) { }

Solution

1. Step 1: Recall constant pattern syntax

   The syntax uses is followed by the constant value to check equality.

2. Step 2: Check each option

   if (x is 10) { } uses if (x is 10), which is correct. Others have syntax errors.

3. Final Answer:

   if (x is 10) { } -> Option C

4. Quick Check:

   Correct constant pattern syntax = if (x is 10) [OK]

Hint: Use 'is' keyword followed by constant value [OK]

Common Mistakes:

• Using assignment '=' instead of 'is'
• Placing 'is' incorrectly
• Adding extra operators

3. What will be the output of the following C# code?

int number = 5;
switch (number)
{
    case 3:
        Console.WriteLine("Three");
        break;
    case 5:
        Console.WriteLine("Five");
        break;
    default:
        Console.WriteLine("Other");
        break;
}

medium

A. Five

B. Three

C. Other

D. No output

Solution

1. Step 1: Identify the value of 'number'

   The variable 'number' is assigned the value 5.

2. Step 2: Match the switch cases

   The switch checks cases 3 and 5. Since number is 5, it matches case 5 and prints "Five".

3. Final Answer:

   Five -> Option A

4. Quick Check:

   number = 5 matches case 5 [OK]

Hint: Match value to case constant exactly [OK]

Common Mistakes:

• Choosing default instead of matching case
• Confusing case values
• Ignoring break statements

4. Identify the error in this C# code using constant patterns:

object obj = 10;
if (obj is 10)
{
    Console.WriteLine("Ten");
}

medium

A. No error, code is correct

B. Missing cast to int before pattern matching

C. Cannot use constant pattern with object type

D. Constant pattern requires a variable after 'is'

Solution

1. Step 1: Understand constant pattern with object

   Constant patterns can be used with object type to check if it equals a constant value.

2. Step 2: Check code correctness

   The code uses obj is 10 correctly to check if obj equals 10. This is valid syntax and logic.

3. Final Answer:

   No error, code is correct -> Option A

4. Quick Check:

   Constant pattern works with object type [OK]

Hint: Constant pattern works directly on object values [OK]

Common Mistakes:

• Assuming cast needed before pattern
• Thinking constant pattern needs variable
• Confusing with type patterns

5. Given a list of integers, which C# code correctly uses constant patterns to count how many times the number 7 appears?

var numbers = new List<int> {1, 7, 3, 7, 5};
int count = 0;
foreach (var n in numbers)
{
    // Fill in the blank
}
Console.WriteLine(count);

hard

A. if (n == 7) count = 7;

B. if (n is not 7) count++;

C. if (n is int) count++;

D. if (n is 7) count++;

Solution

1. Step 1: Understand the goal

   We want to count how many times 7 appears in the list.

2. Step 2: Use constant pattern to check for 7

   The correct constant pattern is if (n is 7) which checks if n equals 7, then increments count.

3. Final Answer:

   if (n is 7) count++; -> Option D

4. Quick Check:

   Constant pattern for 7 increments count [OK]

Hint: Use 'is' with constant to check exact value [OK]

Common Mistakes:

• Assigning count instead of incrementing
• Checking type instead of value
• Counting non-7 values