Understanding Computers and Programming Basics

1. Chapter 1: Introduction to Computers and Programming Starting Out with C++ Early Objects Seventh Edition by Tony Gaddis, Judy Walters, and Godfrey Muganda (Revisions by EL Jones, Ph.D., Florida A&M University)

2. Topics 1.1 Why Program? 1.2 Computer Systems: Hardware and Software 1.3 Programs and Programming Languages 1.4 What Is a Program Made of? 1.5 Input, Processing, and Output 1.6 The Programming Process

3. 1.1 Why Program? Computer – programmable machine designed to follow instructions Program – instructions in computer memory to make it do something Programmer – person who writes instructions (programs) to make computer perform a task SO, without programmers, no programs; without programs, the computer cannot do anything

4. 1.2 Computer Systems: Hardware and Software Main Hardware Component Categories • Central Processing Unit (CPU) • Main memory (RAM) • Secondary storage devices • Input Devices • Output Devices

5. Main Hardware Component Categories

6. Central Processing Unit (CPU) Includes • Control Unit • Retrieves and decodes program instructions • Coordinates computer operations • Arithmetic & Logic Unit (ALU) • Performs mathematical operations

7. The CPU's Role in Running a Program Cycle through: • Fetch: get the next program instruction from main memory • Decode: interpret the instruction and generate a signal • Execute: route the signal to the appropriate component to perform an operation

8. Main Memory • Holds both program instructions and data • Volatile – erased when program terminates or computer is turned off • Also called Random Access Memory (RAM)

9. 8 bits 0 1 1 0 0 1 1 1 1 byte Main Memory Organization • Bit • Smallest piece of memory • Stands for binary digit • Has values 0 (off) or 1 (on) • Byte • Is 8 consecutive bits • Word • Usually 4 consecutive bytes • 32-bit computers • 64-bit computers (contemporary)

10. Secondary Storage • Non-volatile - data retained when program is not running or computer is turned off • Comes in a variety of media • magnetic: floppy or hard disk drive, internal or external • optical: CD or DVD drive • flash: USB flash drive

11. Input Devices • Used to send information to the computer from outside • Many devices can provide input • keyboard, mouse, microphone, scanner, digital camera, disk drive, CD/DVD drive, USB flash drive

12. Output Devices • Used to send information from the computer to the outside • Many devices can be used for output • Computer screen, printer, speakers, disk drive, CD/DVD recorder, USB flash drive

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14. Software Programs That Run on a Computer • Operating system software … programs that • manage hardware resources and programs on computer • how many programs can run at once? • Single tasking - one program at a time (MS-DOS) • Multitasking – multiple programs (UNIX,Windows,OS X) • how many people can use computer at the same time? • Single user – MS-DOS, early versions of Windows • Multiuser - UNIX • Application software • programs that provide services to the user. Ex: word processing, games, programs to solve specific problems

15. 1.3 Programs and Programming Languages • Program a set of instructions directing a computer to perform a task • Programming Languages “15 languages you need to know in 2015” Java JavaScript C# PHP C++ Python C SQL Ruby Objective-C Perl .NET Visual Basic R Swift

16. Programs and Programming Languages Types of languages • Low-level: used for communication with computer hardware directly. • High-level: closer to human language

17. Compilation: from a High-level Program to an Executable File (e.g., hello.run)

18. From a High-level Program to an Executable File • Create file containing the program with a text editor (e.g., pico). • Run preprocessor to convert source file directives to source code program statements (#include lines). • Run compiler to convert source program statements into machine instructions (g++).

19. From a High-level Program to an Executable File • Run linker to connect hardware-specific library code to machine instructions, producing an executable file. (g++) Steps b) through d) are often performed by a single command or button click. Errors occurring at any step will prevent execution of the step that follows.

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21. 1.4 What Is a Program Made Of? Common elements in programming languages: • Key/reserved words (predefined meaning) • Programmer-defined identifiers (rules apply) • Operators (e.g., + for “add, * for multiply) • Punctuation (symbols that organize, e.g., comma (,), semicolon(;), parentheses, etc.) • Syntax ( rules of “grammar” )

22. Example Program 1 #include <iostream> using namespace std; int main() { int num1 = 5, num2, sum; num2 = 12; sum = num1 + num2; cout << "The sum is " << sum; return 0; }

23. Example Program 2 #include <iostream> using namespace std; int main() { int num1 = 5, num2, sum; cout << “Enter second number: “; cin >> num2 sum = num1 + num2; cout << “The sum is “ << sum; return 0; }

24. Key Words • Also known as reserved words • Have a special meaning in C++ • Can not be used for another purpose • Written using lowercase letters • Examples in program (shown in green): using namespace std; int main()

25. Programmer-Defined Identifiers • Names made up by the programmer • Not part of the C++ language • Used to represent various things, such as variables (memory locations) • Example in program (shown in green): double num1

26. Variables • A variable is a name for a cell in computer memory (RAM) where a value can be stored. • The memory cell (variable) holds a data value • A variable must be defined (established / “born” / declared) before it can be used • Example variable definition (declaration): - double num1;

27. Operators • Used to perform operations on data • Many types of operators • Arithmetic: +, -, *, / • Assignment: = • Input: >> - Output: << • Examples in program (shown in green): num2 = 12; sum = num1 + num2; cin >> num2; cout << sum;

28. Punctuation • Characters that mark the end of a statement, separate items in a list, and separate elements of a statement. • Example in program (shown in green): int main ( ) { double num1, num2=3, num3; num1=5; cout << sqrt(num2); }

29. Lines vs. Statements In a source (.cpp) file, A line is all of the characters entered before a carriage return (ENTER key). Blank lines improve the readability of a program. Here are four sample lines. Line 3 is blank: double num1 = 5, num2, sum; num2 = 12; sum = num1 + num2;

30. Lines vs. Statements In a source file, A statement is an instruction to the computer to perform an action. A statement may contain keywords, operators, programmer-defined identifiers, and punctuation. A statement may fit on one line, or it may occupy multiple lines. Here is a single statement that uses two lines: double num1 = 5, num2, sum;

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32. 1.5 IPO: Input-Process-Output Most programs fit this model: (add3.cpp) • Input: Gather input data • from keyboard • from files on disk drives • Process the input data • Output: Display or save the results as output • send it to the screen/monitor or printer • and/or write it to a file

33. 1.6 The Programming Process • Define what the program is to do. • Visualize the program running on the computer (design the “dialogue/conversation” between the program and the user. • Use design tools to create a model of the program. Hierarchy charts, flowcharts, pseudocode, etc. • Check the model for logical errors. • Write the program source code.

34. 1.6 The Programming Process • Compile the source code. 7. Correct any errors found during compilation (debug syntax bugs). 8. Link the program to create an executable file. 9. Run the program using test data for input. 10. Correct any errors found while running the program (debug logic bugs). Repeat steps 4 - 10 as many times as necessary.

35. The Programming Process (cont.) 11. Validate the results of the program. Does the program do what was defined in step 1? Software testing – specialized career path.

36. 1.6 The Programming Process 1. Define what the program is to do. a) Goal: Calculate income tax on income, given a tax rate. b) Make examples to clarify: Tax rate 10%, income 10,000  tax = 1,000. Tax rate 0% (??), income 40,000  tax = 0 Tax rate 1.5% (??), income 500  tax = 7.50

37. 1.6 The Programming Process • Visualize the program running on the computer ( “dialogue/conversation” between the program and the user) a) How does program ask for inputs? Note: etiquette demands requesting it clearly. Please enter income:  this is called a PROMPT Please enter tax rate: Please enter tax rate (0.0– 100.0): (better?) Please enter tax rate (0.00 – 1.00): (better?) Please enter tax rate (5% as 0.05): (best?) b) How does program display outputs? Note: etiquette demands labeling it clearly. 7.50 (never!!) Tax = 7.50 (better?)

38. 1.6 The Programming Process • Use design tools to create a model of the program. Informal steps (pseudo-code) 1. Read tax rate 2. Read income 3. Calculate tax = income * (tax rate) 4. Display the amount of tax. • Check the model for logical errors. Desk check by re-calculating using the examples from step 1.

39. Standard Program Shell (starter) #include <iostream> using namespace std; int main() { // Declare variables. // I: Read inputs. // P: Perform calculations. // O: Display outputs return 0; }

40. 1.6 The Programming Process 5. Write the program source code (coding). What’s needed in the program: 1. standard program shell 2. Variables for inputs, output: - what type of value (decimal, float in C++) - syntax for declaring a variable: <datatype> <variablename>; 3. Input statements with prompts (etiquette) 4. Calculation statements (algebraic formula) - syntax for “assignment statement”: variable = <arithmetic expression>; 5. Output statements with labels (etiquette)

41. 1.6 The Programming Process (on your own) • Compile the source code. 7. Correct any errors found during compilation (debug syntax bugs). 8. Link the program to create an executable file. 9. Run the program using test data for input. 10. Correct any errors found while running the program (debug logic bugs). Repeat steps 4 - 10 as many times as necessary. 11. Validate the results of the program. Does the program do what was defined in step 1?

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43. Chapter 1: Introduction to Computers and Programming Starting Out with C++ Early Objects Seventh Edition by Tony Gaddis, Judy Walters, and Godfrey Muganda