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

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of type pattern matching with 'is' and 'not'

What is the output of this C# code snippet?

C Sharp (C#)

object obj = 42;
if (obj is not string s)
{
    Console.WriteLine("Not a string");
}
else
{
    Console.WriteLine($"String: {s}");
}

A Not a string

B String: 42

C Compilation error

D No output

💡 Hint

Remember that 'is not' checks if the object is NOT of the specified type.

The variable 'obj' holds an int (42), which is not a string. The pattern 'obj is not string s' evaluates to true, so the first branch runs, printing 'Not a string'.

❓ Predict Output

intermediate

Output of switch expression with type patterns

What will this C# switch expression output?

C Sharp (C#)

object val = 3.14;
string result = val switch
{
    int i => $"Integer {i}",
    double d => $"Double {d}",
    _ => "Unknown"
};
Console.WriteLine(result);

A Integer 3

B Unknown

C Double 3.14

D Compilation error

💡 Hint

Check the runtime type of 'val' and which pattern matches first.

The variable 'val' holds a double 3.14, so the pattern 'double d' matches and returns 'Double 3.14'.

🔧 Debug

advanced

Identify the error in type pattern usage

This code snippet causes a compilation error. What is the cause?

C Sharp (C#)

object obj = "hello";
if (obj is int i && i > 0)
{
    Console.WriteLine(i);
}

A No error, code compiles fine

B The variable 'i' is not declared before use

C The 'is' pattern cannot be combined with '&&' operator

D Cannot use relational operator '>' on 'int' in pattern matching

💡 Hint

Try compiling and running the code to see if it works.

The code compiles fine. The pattern 'obj is int i' checks if obj is int and assigns to i. The '&& i > 0' is a valid condition. Since obj is a string, the if block does not run, but no error occurs.

❓ Predict Output

advanced

Output of nested type patterns with property patterns

What is the output of this C# code?

C Sharp (C#)

record Point(int X, int Y);
object obj = new Point(3, 4);
string output = obj switch
{
    Point { X: 3, Y: 4 } p => $"Point at (3,4)",
    Point p => $"Point at ({p.X},{p.Y})",
    _ => "Unknown"
};
Console.WriteLine(output);

A Compilation error

B Point at (0,0)

C Unknown

D Point at (3,4)

💡 Hint

Look at the property pattern matching inside the switch.

The object is a Point with X=3 and Y=4, so the first pattern matches exactly and returns 'Point at (3,4)'.

❓ Predict Output

expert

Output of complex pattern matching with 'or' and 'and' patterns

What is the output of this C# code snippet?

C Sharp (C#)

object val = 10;
string result = val switch
{
    int i and (> 0 and < 5) => "Between 1 and 4",
    int i and (>= 5 or < 0) => "Outside 1 to 4",
    _ => "Other"
};
Console.WriteLine(result);

A Between 1 and 4

B Outside 1 to 4

C Other

D Compilation error

💡 Hint

Check how the 'and' and 'or' patterns combine conditions.

The value 10 is an int and matches the second pattern: int i and (>= 5 or < 0). Since 10 >= 5, it returns 'Outside 1 to 4'.