Relational patterns in C Sharp (C#) - Mini Project: Build & Apply

Relational patterns

📖 Scenario: You are building a simple program to check the age of a person and categorize them as a child, teenager, adult, or senior.

🎯 Goal: Create a program that uses relational patterns in a switch expression to print the correct age category based on the person's age.

📋 What You'll Learn

Create an integer variable age with the exact value 25.

Create a string variable category to hold the age group.

Use a switch expression with relational patterns to assign the correct category:

< 13 is "Child"

< 20 is "Teenager"

< 65 is "Adult"

Anything else is "Senior"

Print the category variable.

💡 Why This Matters

🌍 Real World

Age categories are used in many apps like games, websites, and services to customize content or permissions.

💼 Career

Understanding relational patterns helps you write clear and concise code for decision making in professional C# development.

1

Create the age variable

Create an integer variable called age and set it to 25.

C Sharp (C#)

# Create an integer variable called age and set it to 25
# Your code here

Hint

Use int age = 25; to create the variable.

2

Create the category variable

Create a string variable called category to hold the age group. Initialize it with an empty string "".

C Sharp (C#)

int age = 25;
// Create a string variable called category and set it to an empty string
# Your code here

Hint

Use string category = ""; to create the variable.

3

Use switch expression with relational patterns

Use a switch expression on the variable age with relational patterns to assign the correct string to category. Use these patterns:
< 13 returns "Child"
< 20 returns "Teenager"
< 65 returns "Adult"
Anything else returns "Senior".

C Sharp (C#)

int age = 25;
string category = "";
// Use a switch expression with relational patterns to assign category
# Your code here

Hint

Use category = age switch { < 13 => "Child", < 20 => "Teenager", < 65 => "Adult", _ => "Senior" };

4

Print the category

Write a Console.WriteLine statement to print the value of the variable category.

C Sharp (C#)

int age = 25;
string category = age switch
{
     "Child",
     "Teenager",
     "Adult",
    _ => "Senior"
};
// Print the category variable
# Your code here

Hint

Use Console.WriteLine(category); to print the result.

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.