Nullable value types in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Nullable value types

Declare nullable value type

↓

Assign value or null

↓

Check HasValue property

↓

Use Value

↓

End

This flow shows how a nullable value type is declared, assigned a value or null, checked for a value, and then used or handled accordingly.

Execution Sample

C Sharp (C#)

int? number = null;
if (number.HasValue)
    Console.WriteLine(number.Value);
else
    Console.WriteLine("No value");

This code declares a nullable int, checks if it has a value, and prints the value or a message if null.

Execution Table

Step	Code Line	Variable 'number'	Condition 'number.HasValue'	Action	Output
1	int? number = null;	null	N/A	Assign null to number
2	if (number.HasValue)	null	False	Go to else branch
3	Console.WriteLine(number.Value);	null	N/A	Skipped
4	Console.WriteLine("No value");	null	N/A	Print message	No value

💡 Condition number.HasValue is false because number is null, so else branch runs and execution ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
number	undefined	null	null	null

Key Moments - 2 Insights

Why can't we directly use 'number' without checking HasValue?

Because 'number' might be null, accessing 'number.Value' without checking HasValue causes an error. See execution_table step 2 where HasValue is false, so we avoid using Value.

What does 'int?' mean in the declaration?

'int?' means the variable can hold either an int value or null. This is shown in execution_table step 1 where number is assigned null.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'number' after step 1?

A 0

B null

C undefined

D HasValue

💡 Hint

Check the 'Variable number' column in row for step 1.

At which step does the program decide to print 'No value'?

A Step 1

B Step 2

C Step 4

D Step 3

💡 Hint

Look at the 'Action' and 'Output' columns in the execution table.

If 'number' was assigned 5 instead of null, what would 'number.HasValue' be at step 2?

A True

B False

C null

D Undefined

💡 Hint

Refer to variable_tracker and the meaning of HasValue property.

Concept Snapshot

Nullable value types allow value types to hold null.
Use syntax: int? number = null;
Check if value exists with HasValue.
Access actual value with Value property.
Always check HasValue before using Value to avoid errors.

Full Transcript

This example shows how nullable value types work in C#. We declare 'int? number' which can hold an int or null. Initially, number is null. We check 'number.HasValue' to see if it has a value. Since it is false, we skip printing the value and print 'No value' instead. This prevents errors from accessing a null value. Nullable types are useful when a value might be missing or undefined.