Property validation logic in C Sharp (C#) - Step-by-Step Execution

Concept Flow - Property validation logic

Start

↓

Set Property Value

↓

Validate Value

↓

Valid

↓

Assign

↓

End

When setting a property, the value is checked. If valid, it is assigned; if not, an error is raised.

Execution Sample

C Sharp (C#)

private int age;
public int Age {
  get => age;
  set {
    if (value < 0) throw new ArgumentException("Age cannot be negative");
    age = value;
  }
}

This code sets an Age property that throws an error if a negative value is assigned.

Execution Table

Step	Action	Value to Set	Validation Result	Property Value	Exception Thrown
1	Set Age to 25	25	Valid	25	None
2	Set Age to -5	-5	Invalid	25	ArgumentException: Age cannot be negative
3	Set Age to 0	0	Valid	0	None
4	Set Age to 100	100	Valid	100	None
5	Set Age to -1	-1	Invalid	100	ArgumentException: Age cannot be negative

💡 Execution stops after each set attempt; invalid values throw exceptions and do not change the property.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
age	0 (default)	25	25	0	100	100

Key Moments - 3 Insights

Why does the property value not change when an invalid value is set?

Because the validation fails and an exception is thrown before assignment, so the old value remains unchanged (see steps 2 and 5 in execution_table).

What happens if the validation condition is missing?

Without validation, any value can be assigned, including invalid ones, which can cause bugs or unexpected behavior.

Why do we throw an exception instead of just ignoring invalid values?

Throwing an exception immediately alerts the programmer or user that something is wrong, preventing silent errors and making debugging easier.

Visual Quiz - 3 Questions

Look at the execution_table, what is the property value after step 3?

A 25

B 0

C 100

D -5

💡 Hint

Check the 'Property Value' column for step 3 in the execution_table.

At which step does the validation fail and an exception is thrown?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look for 'Invalid' in 'Validation Result' and 'ArgumentException' in 'Exception Thrown' columns.

If we remove the validation check, what would happen when setting Age to -5?

A An exception is still thrown

B Age remains unchanged

C Age becomes -5 without error

D The program crashes immediately

💡 Hint

Without validation, the setter assigns the value directly (see concept_flow).

Concept Snapshot

Property validation logic in C#:
- Use a private field to store value.
- In the property setter, check the value.
- If invalid, throw an exception.
- If valid, assign to the field.
- This prevents invalid data from being stored.

Full Transcript

This example shows how property validation works in C#. When you try to set a property, the setter checks if the value is valid. If the value is negative for Age, it throws an exception and does not change the stored value. Valid values update the property normally. This helps keep data correct and prevents errors. The execution table shows each step: setting values, validation results, and exceptions if any. The variable tracker shows how the internal age field changes only on valid assignments. Key moments explain why invalid values don't change the property and why exceptions are useful. The quiz tests understanding of these steps.