Creating and Understanding Simple C++ Programs

Chapter 2

Basic Elements of C++

This video is part 1 of 3 in an overview of chapter 2. Each part is about 30 minutes.

• Computer program: A sequence of statements whose objective is to accomplish a task.
• Programming: The process of planning and creating a program.
• Real-world analogy: a recipe for cooking.

Example C++ Program

/*
 * Given the length and width of a rectangle, this program
 * computes and outputs the perimeter and area of the rectangle.
 *
 * by D.S. Malik
 */
#include <iostream>
using namespace std;

int main()
{
    // Variables
    double length;
    double width;
    double area;
    double perimeter;

    // Output Statement
    cout << "Computes and shows a rectangle's  perimeter and area." << endl;

    // Assignment Statements
    length = 6.0;
    width = 4.0;
    perimeter = 2 * (length + width);
    area = length * width;

    // Output Statements
    cout << "Length = " << length << endl;
    cout << "Width = " << width << endl;
    cout << "Perimeter = " << perimeter << endl;
    cout << "Area = " << area << endl;

    return 0; // Return statement
}

Runtime Output

Program to compute and show the parameter and area of a rectangle.
Length = 6
Width = 4
Perimeter = 20
Area = 24

Watch the video to learn about the above program, including comments, variables, assignment statements, output statements, and the return statement.

• Variable: a memory location whose contents can be changed.
• Function: collection of statements; when executed, accomplishes something
  • May be predefined or standard
• Syntax rules: rules that specify which statements (instructions) are legal or valid
• Semantic rules: determine the meaning of the instructions
• Programming language: a set of rules, symbols, and special words

Comments

Comments are for the reader, not the compiler.

• Two types:
  1. Single line: begin with //

     // This is a C++ program.
     // Welcome to C++ Programming.

  2. Multiple line: enclosed between /* and */

     /*
        You can include comments that can
        occupy several lines.
      */

• Always put a comment at the top of your source code with program description and you name.

Special Symbols

• Token: the smallest individual unit of a program written in any language
• C++ tokens include special symbols, word symbols, and identifiers
• Special symbols in C++ include: +, -, *, /, ., ;, ?, ,, <=, !=, ==, >=

Reserved Words (Keywords)

• Cannot be redefined within program
• Cannot be used for anything other than their intended use
• Examples: int, float, double, char, const, void, return

Identifiers

• Identifier: the name of something that appears in a program
  • Consists of letters, digits, and the underscore character (_)
  • Must begin with a letter or underscore
• C++ is case sensitive. NUMBER is not the same as number.
• Two predefined identifiers are cout and cin
• Unlike reserved words, predefined identifiers may be redefined, but it is not a good idea.
• Legal identifiers in C++ include first, conversion, payRate.
• Illegal identifier examples:

  Illegal Identifier	Description
  employee Salary	There can be no space between employee and Salary.
  hello!	The exclamation mark cannot be used in an identifier.
  one+two	The symbol + cannot be used in an identifier.
  2nd	An identifier cannot begin with a digit.

Whitespace

• Every C++ program contains whitespaces, including blanks, tabs, and newline characters.
• Used to separate special symbols, reserved words, and identifiers.
• Proper utilization of whitespaces is important.
  • Can be used to make the program more readable.

Data Types

Data type: a set of values together with a set of operations.

C++ data types fall into three categories:

1. Simple data types, which also have 3 categories:

   1. Integral: integers (numbers without a decimal). Can be categorized further into signed or unsigned. Unsigned means does not have a - or + sign (cannot be negative).

      Data Type	Values	Storage (in bytes)
      bool	true and false	1
      char	–128 to 127	1
      int	–2,147,483,648 to 2,147,483,647	4

   2. Floating-point: decimal numbers. C++ uses scientific notation to represent real numbers (floating-point notation)

      Decimal	Scientific	C++ Floating-Point
      75.924		7.5924E1
      0.18		1.8000E-1
      0.0000453		4.5300E-5
      -1.482		-1.482E0
      7800.0		7.8000E3

      Data Type	Values	Storage (in bytes)
      float	- to	4
      double	– to	8

      Minimum and maximum values of data types are system dependent.

      • Precision: maximum number of significant digits
        • float values are called single precision
        • double values are called double precision

   3. Enumeration types: user-defined data types

2. Structured data types: a collection of a fixed number of components (called members), that are accessed by name.

3. Pointers - Not covered in the course.

Variables

To declare a variable, must specify the data type it will store.

• Syntax: dataType identifier;
• Examples:

  int counter;
  double interestRate;
  char grade;

• Assignment statements: variable = expression
  interestRate = 0.05;

Simple Example Program: Area of a Circe

Before watching, make sure you have installed the required software in Getting Started - Software Setup.

Follow along with this video to create and run the demonstrated program. On your own, add to it the functionality to calculate and display the circumference.

Important

When following along with the video below, type codium in the command line instead of code. Unlike the video, we are using VSCodium instead of Visual Studio Code.

Important

This video describes using VSCode. Instead of what is shown, open your code in VSCodium by typing codium circleArea.cpp instead of code circleArea.cpp.