Computer Programming Putting the machine under our command

Definition of a Program A collection of instructions that describe a task, or set of tasks, to be carried out by a computer

Types of Computer Programs Firmware Systems Software Applications Software

Programming Languages A programming language is an artificial language that can be used to control the behavior of a machine.

Early Computer Programming The first computers were programmed by changing the wiring

Programming Language Background John von Neumann - stored program Alan Turing - Turing Machine Alonzo Church - Lambda calculus

First Generation Languages Machine level code Binary Univac & IBM 701 Add reg 1 to reg 2 place results in reg

Second Generation Languages Assembly code Mnemonic code to represent instructions Move 61 to register named “al” mov al, 061

Third Generation Languages Use English-like terms Compiler to translate to machine level Fortran, ALGOL, COBOL early examples COMPUTE NET-PAY = GROSS-PAY - TOTAL-TAX

Fourth Generation Languages More oriented toward problem solving State the problem, don’t care how it is solved. Divided into categories SQL - Structured Query Language Select * from Employee where Last-Name = “Smith”

Fifth Generation Languages Set of constraints rather than steps to solve problems Heuristics Artificial Intelligence Prolog cat(tom) |- true

Program Development Life Cycle Step 5 Finishing the Project Step 4 Debugging Step 3 Coding Step 2 Making a Plan Step 1 Describing the Problem

Step 1 : Describing the Problem The problem statement is: The starting point of programming A description of tasks the program is to accomplish How the program will execute the tasks Created through interaction between the programmer and the user The program statement includes error handling and a testing plan

PROGRAM GOAL: To compute the total pay for a fixed number of hours worked at a parking garage. INPUTS: Number of Hours Worked a positive number OUTPUTS: Total Pay Earned a positive number PROCESS: The Total Pay Earned is computed as $7.32 per hour for the first eight hours worked each day. Any hours worked beyond the first eight are billed at $11.73 per hour. ERROR HANDLING: The input Number of Hours Worked must be a positive real number. If it is a negative number or other non-acceptable character, the program will force the user to re-enter the information. TESTING PLAN:INPUTOUTPUTNOTES 88*7.32Testing positive input 33*7.32Testing positive input 128* *11.73Testing overtime input –6–6Error message/ask user to re-enter value Handling error Parking Garage Example

Step 2: Developing an Algorithm Algorithm development: A set of specific, sequential steps that describe what the computer program must do Complex algorithms include decision points: Binary (yes/no) Loop (repeating actions) Visual tools used to track algorithm and decision points: Head off to cafe Buy textbook Go to accounting lecture YesNo Yes Wake Up Check wallet for $ Do I have > $80 Go get gas Did I get $80 from the ATM? Do I have my credit card? Go to the ATM for cash

Flowchart and Pseudocode Underlined words are information items that appear repeatedly in the algorithm. 1. Ask the user how many hours they worked today 2. If the number of hours worked < = 8, compute total pay without overtime otherwise, compute total pay with overtime pay 3. Print total pay Bold terms show actions that are common in programming, such as reading data, making decisions, printing, and so on. Flowchart Pseudocode

Step 3: Coding Coding is translating an algorithm into a programming language Generations of programming languages

Compilation Compilation is the process of converting code into machine language Compiler reads the source code and translates it into machine language After compilation, programmers have an executable program

Interpreter Interpreter translates source code into a line by line intermediate form Each line is executed before the next line is compiled Programmers do not have to wait for the entire program to be recompiled each time they make a change. Programmers can immediately see the results of changes as they are making them in the code.

Step 4: Debugging Running a program to find errors is known as debugging Sample inputs are used to determine runtime (logic) errors Debugger: Tool that helps programmers locate runtime errors

Step 5: Finishing the Project Users test the program (internal testing) Beta version released: Information collected about errors before final revision Software updates (service packs): Problems found after commercial release Documentation created: User manuals User training

Programming Languages Selecting the right language: Space available Speed required Organizational resources available Type of target application Visual Basic C / C++ Java HTML JavaScript VBScript ASP / JSP Flash / XML

The CPU: Processing Digital Information CPU is the brains of the computer Different types of CPUs Intel and AMD chips: Used in most Windows-based PCs Apple systems use different CPU design Differentiating CPUs Processing power Clock speed and cache

Instruction Set All commands that the CPU can execute Arithmetic Logic Data Control flow

Instruction Set Architecture CISC Complex Instruction Set Computer Many different instructions Intel - Windows RISC Reduced Instruction Set Computer Fewer instructions Motorola/Intel - Macintosh

The CPU Machine Cycle Fetch The program’s binary code is “fetched” from its temporary location in RAM and moved to the CPU Decode The program’s binary code is decoded into commands the CPU understands. Execute The ALU performs the calculations. Store The results are stored in the registers

The System Clock Located on the motherboard Controls the CPU’s processing cycles Clock cycle Pulse or tick Clock speed Number of pulses per second Measured in hertz (Hz)

The Control Unit Manages the switches inside the CPU Is programmed by CPU designers to remember the sequence of processing stages for that CPU Moves each switch to its correct setting (on or off) and then performs the work of that stage

The Arithmetic Logic Unit (ALU) Part of the CPU designed to perform mathematical operations (addition, subtraction, multiplication, division, etc.) Also performs logical OR, AND, and NOT operations Is fed data from the CPU registers Word size: Number of bits a computer can work with at a time

Cache Memory Small amount of memory located on the CPU chip or near it Stores recent or frequently used instructions and data Used for quick access by the CPU Different levels of cache

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