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.