Relational patterns in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of relational pattern matching with switch

What is the output of this C# code using relational patterns in a switch expression?

C Sharp (C#)

int number = 15;
string result = number switch
{
    < 10 => "Less than 10",
    >= 10 and <= 20 => "Between 10 and 20",
    > 20 => "Greater than 20",
    _ => "Unknown"
};
Console.WriteLine(result);

A Less than 10

B Unknown

C Greater than 20

D Between 10 and 20

💡 Hint

Check which relational pattern matches the value 15.

The value 15 matches the pattern '>= 10 and <= 20', so the output is 'Between 10 and 20'.

❓ Predict Output

intermediate

Result of relational pattern in if statement

What will be printed by this C# code that uses relational patterns in an if statement?

C Sharp (C#)

int age = 65;
if (age is > 60)
{
    Console.WriteLine("Senior");
}
else
{
    Console.WriteLine("Not senior");
}

A Senior

B No output

C Compilation error

D Not senior

💡 Hint

Check if the age is greater than 60.

The age 65 is greater than 60, so the condition is true and 'Senior' is printed.

❓ Predict Output

advanced

Output of nested relational patterns in switch

What is the output of this C# code using nested relational patterns in a switch expression?

C Sharp (C#)

int score = 85;
string grade = score switch
{
    < 60 => "F",
    >= 60 and < 70 => "D",
    >= 70 and < 80 => "C",
    >= 80 and < 90 => "B",
    >= 90 => "A",
    _ => "Invalid"
};
Console.WriteLine(grade);

A C

B A

C B

D D

💡 Hint

Find the range where 85 fits.

85 is between 80 and 90, so the grade is 'B'.

❓ Predict Output

advanced

Value of variable after relational pattern matching

What is the value of the variable 'category' after running this C# code?

C Sharp (C#)

int temperature = 0;
string category = temperature switch
{
    < 0 => "Freezing",
    >= 0 and < 15 => "Cold",
    >= 15 and < 25 => "Warm",
    >= 25 => "Hot",
    _ => "Unknown"
};

A "Cold"

B "Warm"

C "Freezing"

D "Hot"

💡 Hint

Check which pattern matches temperature 0.

0 is >= 0 and < 15, so category is 'Cold'.

❓ Predict Output

expert

Output of complex relational pattern with property

What is the output of this C# code using relational patterns with a property in a switch expression?

C Sharp (C#)

record Product(string Name, decimal Price);

Product item = new("Book", 19.99m);
string priceCategory = item switch
{
    { Price: < 10 } => "Cheap",
    { Price: >= 10 and <= 20 } => "Moderate",
    { Price: > 20 } => "Expensive",
    _ => "Unknown"
};
Console.WriteLine(priceCategory);

A Cheap

B Moderate

C Expensive

D Unknown

💡 Hint

Look at the Price property and see which range 19.99 fits.

The Price 19.99 is between 10 and 20 inclusive, so the output is 'Moderate'.

Practice

1. What does the relational pattern is > 10 check in C#?

easy

A. If a value is greater than 10

B. If a value is equal to 10

C. If a value is less than 10

D. If a value is not equal to 10

Solution

1. Step 1: Understand the relational pattern syntax

   The pattern is > 10 checks if a value is greater than 10.

2. Step 2: Compare with other options

   Options A, B, and D check less than, equality, or inequality, which are different from > 10.

3. Final Answer:

   If a value is greater than 10 -> Option A

4. Quick Check:

   Relational pattern is > 10 means greater than 10 [OK]

Hint: Relational patterns use normal math signs like >, <, == [OK]

Common Mistakes:

• Confusing > with >= or ==.
• Thinking it checks equality instead of comparison.
• Mixing up less than and greater than signs.

2. Which of the following is the correct syntax to check if an integer n is less than or equal to 5 using a relational pattern?

easy

A. if (n is <= 5) { }

B. if (n <= 5) { }

C. if (n is < = 5) { }

D. if (n is <=5) { }

Solution

1. Step 1: Identify correct relational pattern syntax

   The relational pattern syntax uses is followed by the operator and value without spaces inside the operator, like is <= 5.

2. Step 2: Check each option

   if (n is <= 5) { } uses correct syntax: if (n is <= 5). if (n <= 5) { } is normal comparison, not a relational pattern. if (n is < = 5) { } has a space between < and = which is invalid. if (n is <=5) { } misses a space after is, which is required.

3. Final Answer:

   if (n is <= 5) { } -> Option A

4. Quick Check:

   Relational pattern syntax: is <= value [OK]

Hint: Relational patterns need 'is' then operator with no spaces inside operator [OK]

Common Mistakes:

• Using normal comparison without 'is'.
• Adding spaces inside the operator like '< ='.
• Omitting space after 'is'.

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

int x = 7;
if (x is >= 5 and < 10)
    Console.WriteLine("In range");
else
    Console.WriteLine("Out of range");

medium

A. No output

B. Out of range

C. In range

D. Compilation error

Solution

1. Step 1: Evaluate the relational pattern condition

   The condition x is >= 5 and < 10 checks if x is between 5 and 9 inclusive. Since x = 7, it satisfies both parts.

2. Step 2: Determine which branch runs

   Because the condition is true, the Console.WriteLine("In range") runs, printing "In range".

3. Final Answer:

   In range -> Option C

4. Quick Check:

   7 is between 5 and 10, so output is "In range" [OK]

Hint: Check both parts of 'and' relational pattern carefully [OK]

Common Mistakes:

• Thinking 'and' means 'or'.
• Ignoring one part of the condition.
• Assuming syntax error due to 'and'.

4. Identify the error in this code snippet using relational patterns:

int score = 85;
switch (score)
{
    case is > 90:
        Console.WriteLine("Excellent");
        break;
    case is >= 80 and < 90:
        Console.WriteLine("Good");
        break;
    default:
        Console.WriteLine("Average");
        break;
}

medium

A. The 'and' keyword is not allowed in switch case patterns

B. Missing braces around case blocks

C. Relational patterns cannot be used in switch cases

D. The pattern 'is > 90' should be 'case > 90:' without 'is'

Solution

1. Step 1: Identify the syntax error in switch case patterns

   Relational patterns in switch statements use syntax like case > 90:, without the is keyword. The code incorrectly uses case is > 90: and case is >= 80 and < 90:.

2. Step 2: Evaluate the options

   The 'and' keyword is not allowed in switch case patterns is incorrect; and is allowed to combine patterns like case >= 80 and < 90:. The pattern 'is > 90' should be 'case > 90:' without 'is' correctly identifies the misuse of is. Relational patterns cannot be used in switch cases is false; relational patterns are supported in switch cases. Missing braces around case blocks is wrong; braces are not required around case contents.

3. Final Answer:

   The pattern 'is > 90' should be 'case > 90:' without 'is' -> Option D

4. Quick Check:

   Switch case relational pattern: case > value, no is [OK]

Hint: No 'is' keyword needed for relational patterns in switch cases [OK]

Common Mistakes:

• Adding 'is' before relational operators in switch cases.
• Thinking 'and' cannot combine patterns in switch cases.
• Confusing switch statements with 'is' patterns.

5. You want to write a method that returns "Child", "Teen", or "Adult" based on age using relational patterns. Which of these switch expressions correctly implements this?

string GetAgeGroup(int age) => age switch
{
    < 13 => "Child",
    >= 13 and < 20 => "Teen",
    _ => "Adult"
};

hard

A. Replace 'and' with '&&' in the second pattern

B. Correct as is

C. Use nested if statements instead of switch

D. Add parentheses around '>= 13 and < 20'

Solution

1. Step 1: Analyze the switch expression with relational patterns

   The switch expression uses relational patterns correctly: < 13 for "Child", combined pattern >= 13 and < 20 for "Teen", and default for "Adult".

2. Step 2: Confirm syntax correctness

   The 'and' keyword is valid in switch expressions for combining patterns. No parentheses or '&&' are needed here.

3. Final Answer:

   Correct as is -> Option B

4. Quick Check:

   Switch expressions support 'and' for combined relational patterns [OK]

Hint: Use 'and' to combine relational patterns in switch expressions [OK]

Common Mistakes:

• Replacing 'and' with '&&' which is invalid in patterns.
• Adding unnecessary parentheses.
• Thinking switch expressions don't support relational patterns.