Introduction to Variables and Data Types

How to work with numeric and string data

• 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.

Arithmetic Operators

• 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.

Assignment Operators

• Syntax: variableName = expression;
• Shortcut assignment operators:
  • += for addition
  • -= for subtraction
  • *= for multiplication
  • /= for division
  • %= for modulus

Casting

• 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()).

Formatting

• 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

Math Class

• 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.

String Data Type

• 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.

NULL Value

• 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.

Using Null Values in Arithmetic Expressions

• 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.

Learn about variables, constants, and scope in programming, including naming conventions and syntax. Understand how to work with numeric and string data.