Overview History Hardware Software Development Life Cycle Programming

Overview • • History Hardware Software Development Life Cycle Programming Languages Structured Programming Defining the Problem cosc 175 - lec 1 1

History of computers • First Generation computers (1951 -1958) – – vacuum tubes used large amounts of electricity, heat, large and expensive 1946 - ENIAC - computed trajectories for U. S. Army 1951 - UNIVAC - first commercially available computer, census • Second Generation computers (1959 -1963) – transistors, less heat – more reliable, less expensive • Third Generation computers (1964 -1970) – integrated circuits – less heat, higher speed cosc 175 - lec 1 2

History of computers • Fourth Generation computers (1971 -present) – – – microprocessor => Personal Computer Apple II (1977), IBM PC (1981) ARPANET (1969) WWW (1991) Today - cheaper, smaller, better • Fifth Generation computers (present and beyond) – Artificial Intelligence • http: //www. history. com/shows/modern-marvels/videos/whoinvented-the-computer#who-invented-the-computer cosc 175 - lec 1 3

Computer Components (Hardware) Peripherals Central Processing Unit ( CPU ) Input Device Control Unit Arithmetic Logic Unit Output Device Auxiliary Storage Device Memory Unit ( RAM & Registers ) cosc 175 - lec 1 4

Software • Systems Software – Operating System – software that controls overall operation of computer – DOS, Windows, Unix, Linux • Programming Environment – Editor/Compiler/Interpreter/Linker/ Debugger • Application Software cosc 175 - lec 1 5

Software Development Life Cycle 1. 2. 3. 4. 5. Define the Problem (Analysis) Design the Solution (Algorithm) Code Solution (Program) Test and Debug Maintain & Document cosc 175 - lec 1 6

SDLC cosc 175 - lec 1 7

1. Analysis What? Defining the Problem Requirements Generate and document a clear problem statement § Need to talk to all stakeholders § Most common cause of software system failure traced to poor requirements gathering § IPO § § cosc 175 - lec 1 8

2. Design • HOW? • Planning • Algorithm – expansion of steps in the IPO diagram • Flowchart • Pseudocode cosc 175 - lec 1 9

Start Pseudocode: Input pay. Rate Input hrs. Worked net. Pay = pay. Rate * hrs. Worked Output net. Pay Stop cosc 175 - lec 1 10

Design tools pseudocode • Can be done easily on word processor • Implements structured • design elements well • Not visual • No standard flowchart • Standardized • visual • Difficult to modify • requires special software to do on computer cosc 175 - lec 1 11

An Algorithm is. . . • Step-by-step procedures for solving a problem in a finite amount of time. • We are learning to write algorithms and the computer is simply a fast and flexible tool for implementing algorithms. • An algorithm is an ordered set of instructions such that: (1) There a finite number of steps. (2) It takes a finite amount of time to execute the steps. (3) Each step is precise in meaning, and “doable. ” (4) It solves a general class of problems. cosc 175 - lec 1 12

3. Code the Solution • Choose language • Edit – create source program • Compile - translate – Syntax error – violate rules of programming language • Link • Create an executable program cosc 175 - lec 1 13

4. Test and Debug • Test with variety of data • Debugging: locating and correcting errors – Logic error or bug - flaw in algorithm • Run-time error e. g. Divide by zero • Programming packages usually have debugger software to help programmer cosc 175 - lec 1 14

5. Maintain and Document • Maintenance – Changing and maintaining existing programs – Most coding is actually maintenance • Documentation – sometimes done by technical writers cosc 175 - lec 1 15

A Tempting Shortcut? DEBUG REVISE DEBUG t? u c t r Sho CODE GOAL TEST THINKING cosc 175 - lec 1 CODE 16

Programming Languages • Definition: languages with strict grammar rules, symbols, and words used to construct a computer program • Machine Languages – is not portable, runs only on specific type of computer – is made up of binary-coded instructions (strings of 0 s and 1 s) – is the language that can be directly used by the computer • Assembly Language – Mnemonic codes are used for the op. codes instead of binary, EXA: LDA N, SUB B – assembly language program must be translated into machine language before it can be executed, ‘assembler’. • High Level Languages – portable – similar to natural language – Requires compiler – translates high-level language into machine code – FORTRAN, Visual BASIC, COBOL, Pascal, Ada, C++, Java – most are standardized by ISO/ANSI cosc 175 - lec 1 17

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Assembly Language cosc 175 - lec 1 19

C++ • • • 1972 : C created by Dennis Ritchie at Bell Labs => 90% of UNIX is then written in C 1983: C++ - Bjarne Stroustrup at Bell Labs 1998 : ISO/ANSI standardization of C++ general-purpose programming language - many uses Flexible - few restrictions high demand for C, C++ programmers high level/low level Portable - leader in portability programmer oriented-"written by a professional programmer for professional programmers" cosc 175 - lec 1 20

1. Edit: write and type the program (source code) in C++ , Save as my. Prog. cpp 2: Compile: translate the source code into machine language => myprog. obj syntax error – violation of the rules of the language. 3: Link = bring in other code from libraries, bind the modules together, etc => my. Prog. exe 4: Run = run the executable file Logic errors (bug) – An error caused by a mistake in programming instructions. A logic error causes a program to operate wrongly or produce incorrect data, but not to stop working cosc 175 - lec 1 21

Structured Programming Ø Top-down Design– divide and conquer § § § Modularity subprograms Stepwise refinement Ø The Structure Theorem- Use 3 basic control structures to solve any problem 1. Sequence 2. Selection (if-then-else) 3. Repetition (loop) cosc 175 - lec 1 22

SEQUENCE Statement Display “Enter Name” Input name Display “Hello “ name cosc 175 - lec 1 23

SELECTION (branch) IF Condition THEN Statement 1 ELSE Statement 2 True Statement 1 Statement Condition . . . False Statement 2 If (num > 0) Display “Positive” Else Display “Negative” cosc 175 - lec 1 24

LOOP (repetition) WHILE Condition DO Statement 1 False Condition . . . Tr ue Statement cosc 175 - lec 1 25

SUBPROGRAM (function). . . SUBPROGRAM 1 a meaningful collection of SEQUENCE, SELECTION, LOOP, SUBPROGRAM cosc 175 - lec 1 26

Computing Profession Ethics • • • copy software only with permission from the copyright holder give credit to another programmer by name whenever using his/her code use computer resources only with permission guard the privacy of confidential data use software engineering principles to develop software free from errors cosc 175 - lec 1 27

As proposed by the project sponsor. As specified in the project request. As produced by the programmers. As installed at the user's site. cosc 175 - lec 1 As designed by the senior analyst. What the user wanted. 28

Step 1: Analysis Define the Problem IPO 1. Input: Determine what is given =>nouns, adjectives 2. Output: Determine what is required =>nouns, adjectives 3. Processing: Determine the transformations needed, actions needed to produce the required output =>verbs, adverbs cosc 175 - lec 1 29

variables • Input and output data • Nouns • Naming convention – No spaces – Meaningful names – Usually begin with lowercase – Examples: room. Width, num. People, student. Name cosc 175 - lec 1 30

Example 1 Read three numbers, add them together and print the total. cosc 175 - lec 1 31

1. Identify inputs Underline nouns Read three numbers, add them together and print the total. • Break up several values into separate variables cosc 175 - lec 1 32

1. Identify inputs fill Input column first Read three numbers, add them together and print the total. • Break up several values into separate variables cosc 175 - lec 1 33

2. Identify outputs output column next Read three numbers, add them together and print the total. • Break up several values into separate variables • No verbs here cosc 175 - lec 1 34

3. Processing-Define processing steps by bolding verbs Read three numbers, add them together and print the total. cosc 175 - lec 1 35

Each verb is a process step Read three numbers, add them together and print the total. Hint: Usually follows: input, process, output cosc 175 - lec 1 36

Step 3: define list of actions Read three numbers, add them together and print the total. • Hint: Use verbs • these steps usually involve the input and output defined in step 1 cosc 175 - lec 1 37

Example 2: Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature. cosc 175 - lec 1 38

Example 2: Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature. cosc 175 - lec 1 39

Example 2: Write a program to prompt the operator for the maximum and minimum temperature readings on a particular day, accept those readings as integers, and calculate and display on the screen the average temperature. cosc 175 - lec 1 40