Type patterns in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Type patterns

Start with object variable

↓

Check type with pattern

↓

Cast and use

↓

End

The program checks if an object matches a type pattern, then uses it if yes, otherwise skips or does other actions.

Execution Sample

C Sharp (C#)

object obj = 42;
if (obj is int number)
{
    Console.WriteLine(number + 10);
}

Checks if obj is an int, assigns it to number, then prints number plus 10.

Execution Table

Step	Action	Evaluation	Result
1	Assign obj = 42	obj holds 42 (int)	obj = 42
2	Check if obj is int	obj is int? True	number = 42
3	Execute inside if	Print number + 10	Output: 52
4	End	No more code	Program ends

💡 After printing 52, program ends as no more code follows.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
obj	null	42 (int)	42 (int)	42 (int)
number	undefined	undefined	42	42

Key Moments - 2 Insights

Why does 'number' get a value only after the type check?

Because 'number' is declared inside the 'if' condition using the type pattern, it only gets assigned if 'obj is int' is true, as shown in execution_table step 2.

What happens if obj is not an int?

The 'if' block is skipped because the type pattern fails, so 'number' is never assigned and the code inside the block does not run, as implied by the 'No' branch in concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the value of 'number'?

A undefined

B null

C 42

D 10

💡 Hint

Check the 'Result' column at step 2 in execution_table where 'number = 42' is assigned.

At which step does the program print output?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the 'Action' and 'Result' columns in execution_table for the printing action.

If obj was a string instead of int, what would happen?

A The if block is skipped, no output printed

B Compilation error

C The if block runs and prints the string plus 10

D The program crashes

💡 Hint

Refer to concept_flow where the 'No' branch skips the block if type pattern fails.

Concept Snapshot

Type patterns check if an object matches a type.
Syntax: if (obj is Type varName) { use varName }
If true, varName holds the casted value.
If false, block is skipped.
Useful for safe type checks and casts.

Full Transcript

This example shows how C# uses type patterns to check an object's type safely. We start with an object variable 'obj' assigned the value 42, which is an int. The 'if' statement uses 'obj is int number' to check if obj is an int. If true, it assigns obj to a new variable 'number' of type int. Inside the 'if' block, we print number plus 10, resulting in 52. If obj was not an int, the block would be skipped and no output printed. This pattern helps avoid manual casting and errors by combining type check and assignment in one step.