C++ Variables and Data Types

Integers and Floating-Point Numbers

• Integers represent whole numbers (positive, negative, or zero), like 10, -5, 0. Floating-point numbers represent numbers with decimal parts, like 3.14, -2.5, 0.0.
• C++ stores integers directly; no special formatting (commas, spaces) is needed.
• Negative integers are represented using the two's complement method.
• Octal (base-8) and hexadecimal (base-16) notations are used to represent integers differently (e.g., 010 octal, 0xA hex).

Variables in C++

• A variable is a named storage location that holds a value. It has a name, type, and value.
• Variable names must adhere to rules:
  • Only letters, digits, and underscores are permitted.
  • Names must begin with a letter or underscore.
  • C++ is case-sensitive (myVar and myvar are different).
• Examples:
  • Valid: count, _total, price1
  • Invalid: 2count, total!, count-1

Variable Declaration

• To create a variable, you must declare its type and name.
• Syntax: data_type variable_name;
• Example: int age; declares an integer variable named age.
• Multiple variables of the same type can be declared on the same line: int x, y, z;

Value Assignment

• The assignment operator (=) assigns a value to a variable. variable_name = value;
• Example: age = 30;
• Assignment is different from comparison (==). x = 5 assigns 5 to x, while x == 5 checks if x is equal to 5.

Reserved Keywords

• Keywords are reserved words with predefined meanings in C++. They cannot be used as variable names.
• Example: int, float, if, else
• Keywords are case-sensitive.

Comments in Code

• Comments explain the purpose of your code.
• Line comments start with //.
• Block comments start with /* and end with */.
• Example:

  // This is a line comment
  /* This is a block comment
  spanning multiple lines */
  

• Nesting comments is not allowed (e.g., /* /* */ */).

Practical Application (LAB)

• Scenario: Improve this poorly-formatted code.

// Function to calculate area
// This is extra, unnecessary comment
int area (int length, int width){
   // Calculat area
  int area =  length* width;
   // return the calculated area
  return area;
}

• Improvements:
  • Remove redundant comments.
  • Improve variable names (e.g., length to rectangleLength).
  • Add or edit comments where needed for clarity (e.g., explaining the calculation).
  • Use consistent formatting for readability (e.g., add white space).