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 701Add reg 1 to reg 2 place results in reg 6 000000 00001 00010 00110 00000 100000
Second Generation Languages
Assembly code
Mnemonic code to represent instructionsMove 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
Prologcat(tom) |- true
Program Development Life Cycle
Step 5Finishing the Project
Step 4Debugging
Step 3Coding
Step 2Making a Plan
Step 1Describing 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: INPUT OUTPUT NOTES
8 8*7.32 Testing positive input
3 3*7.32 Testing positive input
12 8*7.32 + 4*11.73 Testing overtime input
–6 Error 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
Yes No
No
No
Yes
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 today2. If the number of hours worked < = 8, compute total pay without overtime otherwise, compute total pay with overtime pay3. 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 manualsUser training
Programming Languages
Selecting the right language:Space availableSpeed requiredOrganizational resources availableType of target application
Visual Basic
C / C++Java HTML
JavaScriptVBScript
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 executeArithmeticLogicDataControl 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 motherboardControls the CPU’s processing cyclesClock cycle
Pulse or tick
Clock speedNumber of pulses per secondMeasured 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 registersWord 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
Software Horror Stories
http://www.cs.tau.ac.il/~nachumd/verify/horror.html