Introduction to Variables and Data Types

Study Notes

Variables store values that can change as a program executes.
- Naming convention: start with a lowercase letter, and capitalize the first letter of each word (camel notation).
- Syntax: type variableName; and variableName = value;
Constants store values that can't be changed.
- Naming convention: capitalize the first letter of each word (Pascal notation).
- Syntax: const type ConstantName = value;
Scope determines what code has access to a variable.
- Method scope: a variable declared within a method is only accessible within that method.
- Class scope: a variable declared within a class but not within a method is accessible by all methods in the class.
- Lifetime of a variable is the period of time it's available for use.

Order of precedence:
1. Increment and decrement
2. Positive and negative
3. Multiplication, division, and modulus
4. Addition and subtraction
Arithmetic expressions can use integer and decimal data types.
Increment and decrement operators can be prefixed or postfixed.

Implicit casting: widening conversion from less precise to more precise data types (e.g., byte to int).
Explicit casting:
- Using the (type) keyword for widening and narrowing conversions.
- Using the Convert class for explicit casting (e.g., ToInt32(value)).
- Using special methods (e.g., ToString(), Parse(), and TryParse()).

Two ways to format numbers:
- Using the ToString() method with format codes (e.g., "c" for currency, "p1" for percentage).
- Using the Format method of the String class with format specifications (e.g., {0:c} for currency).
Standard format codes:
- c for currency
- p1 for percentage
- n0 for number with thousands separator
- f3 for fixed-point notation with three decimal places

The Math class provides methods for mathematical operations.
Five common methods:
1. Round() for rounding decimal numbers with optional precision and mode.
2. Pow() for raising a number to a power.
3. Sqrt() for calculating the square root of a number.
4. Min() and Max() for finding the minimum and maximum of two numbers.### Math Class
The Math.Round method can be used to round a number to a specified number of decimal places.
The Math.Round method can also be used to round a number to a whole number.
The Math.Pow method can be used to calculate the power of a number.
The Math.Sqrt method can be used to calculate the square root of a number.
The Math.Max method can be used to find the maximum value between two numbers.
The Math.Min method can be used to find the minimum value between two numbers.

A string can be declared and initialized using the string keyword.
A string can be initialized with a value or as an empty string.
A string can be initialized as null to indicate an unknown value.
Strings can be joined using the + operator.
Strings can be joined with a value data type, and C# will automatically convert the value to a string.
Escape sequences can be used in strings to represent special characters such as newline (\n), tab (\t), return (\r), backslash (\\), and quotation (\").
Verbatim string literals can be used to code strings that contain special characters, and can be specified using the @ symbol.

A nullable type is a value type that can store a null value.
Nullable types are used to indicate that the value of a variable is unknown.
There are three ways to declare a nullable type: Nullable variableName [= expression];, type? variableName [= expression];, and type ? variableName [= expression];.
Nullable types have two properties: HasValue and Value.
The HasValue property returns a true value if the nullable type contains a value, and a false value if it is null.
The Value property returns the value of the nullable type.
The null-coalescing operator (??) can be used to assign a default value to a nullable type if it is null.

If a nullable type is used in an arithmetic expression and its value is null, the result of the expression is always null.
The null-coalescing operator (??) can be used to assign a default value to a nullable type in an arithmetic expression.