Using identifiers

They are the names used to identify the elements in programs. e.g., namespaces, classes, methods and variables.
- Only letters (uppercase and lowercase), digits and underscore characters can be used.
- An identifier shall start with a letter or underscore.

Using variables

Do not start with underscore (_). It will limit the interoperability with other languages.
Do not create identifiers that differ only by case. It can be consfusing and also limit the interoperability with other languages.
Start the name with a lowercase letter.
In a multiword identifier, use camelCase notation.
Do not use Hungarian notation.

// A variable can be declared and then initialized in different lines
int age;
age = 42;
// Or not
int height = 172;

A variable contains a random value until you assign a value to it.
C# does not allow the use of unassigned variables. This is called definite assignment rule.

Data type	Description	Size(bits)	Example
`int`	integers	32	`int age = 34;`
`long`	integers (bigger range)	64	`long age = 34L;`
`float`	floating-point numbers	32	`float age = 34.00F;`
`double`	Double-precision floating-point numbers	64	`double age = 34.00;`
`decimal`	Monetary values	128	`decimal age = 34.00M;`
`string`	Sequence of characters	16 (per character)	`string age = "34";`
`char`	Single character	16	`char age = '3';`
`bool`	Boolean	8	`bool isOld = false;`

It is more efficient and replaces the operand + for string concatenaton.
The symbol $ at the start of the string indicates that:
- It is an interpolated string
- The expression between { } should be evaluated and the result substituted in their place.

Console.WriteLine("Nome: " + user.Name.Text + "Age: " + user.age.Text);

Console.WriteLine($"Nome: {userName.Text}, Age: {user.age.Text}");