1.1.8 How to Identify Field Types When Assigning

• 2.1i Choosing Variable and Field Types (13.3)

An Assignment Must Use a Value That Fits the Field

A supplied class can contain fields with different types.

Conceptually, a Player type might include:

string name;
int jerseyNumber;
bool isAvailable;

Those declarations tell you what kind of information each field is designed to hold.

Before assigning a value, identify the field's type.

Then choose a compatible value.

Read the Field Declaration

Suppose the supplied source contains:

string name;

The field type is:

string

A compatible text value can look like:

"Jordan"

Now consider:

int jerseyNumber;

The field type is:

int

A compatible whole-number value can look like:

7

For:

bool isAvailable;

a compatible Boolean value is:

true

or:

false

Match UML Values to C# Types

A UML object diagram might show:

player1 : Player
-------------------------
name = "Jordan"
jerseyNumber = 7
isAvailable = true

The values suggest different kinds of data:

"Jordan" → text
7        → whole number
true     → Boolean

The supplied class should contain compatible field types for the model.

The UML gives you the intended state.

The C# field declaration tells you the type expected by the source.

Quotation Marks Matter

Compare:

"7"

with:

7

The first is text.

The second is a numeric value.

If the field is:

int jerseyNumber;

then:

7

matches the intended whole-number type more directly than:

"7"

Do not choose quotation marks based on how the value looks.

Choose the representation based on the field type.

Boolean Values Are Not Quoted Text

For:

bool isAvailable;

the Boolean literal is:

true

not:

"true"

The quoted version is a string.

This difference is easy to miss because both are readable words.

C# treats them as different kinds of values.

Use the Supplied Class as the Type Authority

When working in an existing project, do not guess a field's type from its name.

A field called:

number

could be represented in several ways depending on the program.

Inspect the supplied declaration.

The code tells you the actual C# type expected by that class.

Do Not Redefine the Class to Make an Assignment Easier

Suppose the supplied field is:

int jerseyNumber;

and you accidentally try to use text.

The solution is not automatically to change the field into:

string jerseyNumber;

The class design may be part of the required source.

Correct the value to match the intended type unless the task explicitly requires a class-design change.

The Compiler Can Reveal Type Mismatches

If you assign an incompatible value, C# may report a compiler error.

Treat the message as evidence.

Ask:

• What type does the field expect?
• What type is the value I supplied?
• What does the requirement or UML say the value should represent?

Then make a focused correction.

Do Not Introduce Conversion Without a Reason

Later programming work may convert values between representations.

At this point, prefer a value that naturally matches the supplied field type.

If the model says:

jerseyNumber = 7

and the field is int, use the whole-number value.

Do not convert from text merely to make the example more complicated.

The Main Mapping

For the basic types already available from FIT:

UML / information       C# type
--------------------------------
text                     string
whole number             int
fractional number        double
true/false               bool

The exact supplied class controls the actual type used in the project.

Your job is to recognize that type and assign information that fits it.