Properties vs fields in C Sharp (C#) - Visual Side-by-Side Comparison

Concept Flow - Properties vs fields

Start

↓

Declare field

↓

Declare property

↓

Access field directly

↓

Access property (get/set)

↓

Field stores data

↓

Property controls access

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End

This flow shows how fields store data directly, while properties provide controlled access to that data.

Execution Sample

C Sharp (C#)

class Person {
  public string name; // field
  private int _age;   // field
  public int Age {    // property
    get { return _age; }
    set { if (value >= 0) _age = value; }
  }
}

Defines a class with a public field and a property that controls access to a private field.

Execution Table

Step	Action	Field 'name'	Field '_age'	Property 'Age' (get/set)	Output/Effect
1	Create Person object	null	0	N/A	Object created, fields default initialized
2	Set name = "Alice"	"Alice"	0	N/A	Field 'name' set directly
3	Set Age = 30	"Alice"	30	set called with 30	Property setter checks and sets _age
4	Get Age	"Alice"	30	get returns 30	Property getter returns _age value
5	Set Age = -5	"Alice"	30	set called with -5	Setter ignores invalid negative value
6	Get Age	"Alice"	30	get returns 30	Age remains 30, no change
7	Access name directly	"Alice"	30	N/A	Direct access to field value
8	Access Age via property	"Alice"	30	get returns 30	Access controlled by property
9	End	"Alice"	30	N/A	Execution ends

💡 Execution stops after demonstrating field direct access and property controlled access.

Variable Tracker

Variable	Start	After 2	After 3	After 5	Final
name	null	"Alice"	"Alice"	"Alice"	"Alice"
_age	0	0	30	30	30
Age (property)	N/A	N/A	set=30	set=-5 ignored	get=30

Key Moments - 3 Insights

Why doesn't setting Age to -5 change the _age field?

Because the property setter checks if the value is negative and ignores it if so, as shown in step 5 of the execution_table.

Can we access the private field _age directly from outside the class?

No, _age is private. We access it only through the Age property, which controls how it is read or changed (see steps 3 and 4).

Why do we use properties instead of public fields?

Properties let us add rules when getting or setting values, like validation or extra logic, unlike fields which store data directly (compare step 2 vs step 3).

Visual Quiz - 3 Questions

Look at the execution_table at step 5. What happens when Age is set to -5?

A The setter ignores the value and _age stays 30

B The _age field is updated to -5

C An error is thrown

D The name field changes

💡 Hint

Check the 'Action' and 'Output/Effect' columns at step 5 in execution_table.

At which step does the property getter return the current age value?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Look for 'get returns' in the Property 'Age' column in execution_table.

If we remove the property setter validation, what would happen at step 5?

A The name field would change

B The _age field would be set to -5

C The _age field would remain 30

D The program would crash

💡 Hint

Refer to variable_tracker and how the setter controls _age changes.

Concept Snapshot

Fields store data directly and are accessed without checks.
Properties provide controlled access with get and set methods.
Use properties to add validation or logic when reading/writing data.
Fields can be public or private; properties usually control private fields.
Access properties like fields but they run code behind scenes.

Full Transcript

This lesson shows the difference between fields and properties in C#. Fields hold data directly and can be accessed or changed without restrictions. Properties act like smart fields: they let you control how data is read or changed by using get and set methods. For example, a property can prevent invalid values from being stored. The execution table traces creating a Person object, setting a public field 'name' directly, and using the Age property to safely set and get a private field '_age'. When trying to set Age to a negative number, the property setter ignores it, keeping the data valid. This helps beginners see why properties are useful for controlling access and adding rules, unlike fields which are simple storage.