Prof. Ken Regis
Institute for Computer Engineering
Florida State University
Oktober 2002
Prof. Ken Regis - FIT 1-1
1
Ken Regis
Why learn about programming?
 programming teaches you how to solve
problems
 programming helps you be more precise
(doesn’t win you many friends though!)
why did the computer scientist stay in the shower forever?
the instructions on the shampoo said “lather, rinse, repeat!”
 programming gets you more out of your
computer
 you may not be programming, but
knowing a little bit about Computer Science
and knowing a little bit about Programming
will help you work with people who do
Programs
 A program is a set of step-by-step instructions
that directs the computer to do the tasks you
want it to do and produce the results you want.
You have already programmed!
 You wrote complex formulas in Excel
=$D5*EKSP(-LN(2)*E$4/$C5)
 You used SQL to talk to databases
SELECT * FROM contacts
WHERE age BETWEEN 18 AND 35;
 You programmed in MATLAB
function r = fz(x)
global M p w1;
X = [cos(x), sin(x); -sin(x), cos(x)];
r1 = M' - p' - X*w1';
r = r1'*r1;
Programming
 Programming consists of two steps:


algorithmic design (the architects)
coding (the construction workers)
 Programming requires:



a programming language to express your ideas
a set of tools to design, edit, and debug your code
either



a compiler to translate your programs to machine code
a machine to run the executable code
or

an interpreter to translate and execute your program
Programming Languages
 A programming language is a set of rules that
provides a way of telling a computer what
operations to perform.
Levels of Programming Languages





Machine language
Assembly Language
High Level Languages
Fourth Generation Languages (4GL)
Fifth Generation Languages (5GL)
Machine Languages
 different for each computer processor
0100
001101 100000 001101 110001
00101 10001 10000
01110
111001
. . .
Assembly Languages
 different for each computer processor
main
proc pay
mov ax, dseg
mov ax, 0b00h
add ax, dx
mov a1, b1
mul b1, ax
mov b1, 04h
High-Level Languages
 Higher Level Languages
 Use traditional programming logic where the
programming instructions tell the computer what to do
and how to perform the required operations.
 4GLs
 Use high-level English-like instructions to specify what
to do, not how to do it .
Types of high level
Programming Languages




Procedure-oriented languages
Object-oriented languages
Event-driven languages
Declarative languages
Procedure-Oriented Languages
 FORTRAN
 COBOL
 Pascal
C
 Ada
OOED Languages
 Object-oriented languages
 Smalltalk
 C++
 Ada 95
 Java
 C#
 Event-driven languages
 Visual Basic
 most Visual languages
Declarative languages (5GL)
 Functional(?): Lisp, Scheme, SML
 Also called applicative
 Everything is a function
 Logic: Prolog
 Based on mathematical logic
 Rule- or Constraint-based
Language
Family
Tree
Lots more Languages
 There are many programming languages out there
 specification languages, e.g. Z, UML
 document languages, e.g. LaTeX, Postscript
 command languages, e.g. csh, MATLAB
 query languages, e.g. SQL
 Scripting languages, e.g. Perl, Python, JavaScript,
VBScript, ASP, PHP, …
What determines a “good”
language
 Formerly: Run-time performance
 (Computers were more expensive than programmers)
 Now: Life cycle (human) cost is more important
 Ease of designing, coding
 Debugging
 Maintenance
 Reusability
 FADS
Why so many?
 Why does some people speak French?
 Most important: the choice of paradigm, and
therefore language, depends on how humans best
think about the problem
 Other considerations:
 efficiency
 compatibility with existing code
 availability of tools
What can a program do?
 A program can only instruct a computer to:
 Sequence
 Calculate
 Store data
 Compare and branch
 Iterate or Loop
 Write Output
 Read Input
Sequence Control Structures
 Sequence control structures direct the order of
program instructions.
 The fact that one instruction follows another—in
sequence—establishes the control and order of
operations.
Calculate
 A program can instruct a
computer to perform
mathematical
operations.
Add 1 to
Counter
Store
 A program will often
instruct a computer to
store intermediate results.
Place 1
in
Counter
Compare and Branch
 A program can instruct a computer to compare two
items and do something based on a match or mismatch
which, in turn, redirect the sequence of programming
instructions.
 There are two forms:
 IF-THEN
 IF-THEN-ELSE
IF-THEN
Entry
Test
condition p
Exit
false
true
True
statement a
IF-THEN-ELSE
Entry
Test
condition p
false
“false”
statement a
true
Exit
“true”
statement a
Iterate
 A program loop is a form
of iteration. A computer
can be instructed to
repeat instructions under
certain conditions.
No
Iteration Control Structures
 Iteration control structures are looping mechanisms.
 Loops repeat an activity until stopped. The location
of the stopping mechanism determines how the loop
will work:
 Leading decisions
 Trailing decisions
Leading Decisions
 If the stop is at the beginning of the iteration, then the
control is called a leading decision.
 The command DO WHILE performs the iteration and
places the stop at the beginning.
DO WHILE Loop
Entry
Exit
No
Test
condition p
Yes
Loop
statement a
Trailing Decisions
 If the stop is at the end of the iteration, the control
mechanism is called a trailing decision.
 The command DO UNTIL performs the iteration and
puts the stop at the end of the loop.
DO UNTIL Loop
Entry
Loop
statement a
Test
condition p
Exit
No
Yes
Programs are Solutions
to Problems
 Programmers arrive at these solutions by using one or
more of these devices:
 Logic flowcharts
 Pseudocode
 Structured Programming
 UML
 Object Oriented Programming
Logic Flowcharts
 These represent the
flow of logic in a
program and help
programmers “see”
program design.
Common Flowchart Symbols
Common Flowchart Symbols
Terminator. Shows the starting and ending points of the program. A terminator has
flowlines in only one direction, either in (a stop node) or out (a start node).
Data Input or Output. Allows the user to inputdata and results to be displayed.
Processing. Indicates an operation performed by the computer, such as a variable
assignment or mathematical operation.
Decision. The diamond indicates a decision structure. A diamond always has two
flowlines out. One flowlineout is labeled the “yes” branch and the other is labeled the
“no” branch.
Predefined Process. One statement denotes a group of previously defined statements.
For instance, “Calculate m!” indicates that the program executes the necessary commands
to compute m factorial.
Connector. Connectors avoid crossing flowlines, making the flowchart easier to read.
Connectors indicate where flowlines are connected. Connectors come in pairs, one with
a flowline in and the other with a flowline out.
Off-page connector. Even fairly small programs can have flowcharts that extend several
pages. The off-page connector indicates the continuation of the flowchart on another
page. Just like connectors, off-page connectors come in pairs.
Flowline. Flowlines connect the flowchart symbols and show the sequence of operations
during the program execution.
Flowchart for a
Cash Register Program
Start
sum=0
Input price
sum=sum+price
Yes
More
items?
No
vat=sum x 0.25
total=sum+vat
Output sum, vat,
and total
Stop
Psuedocode
 This device is not visual but is considered a “first draft”
of the actual program.
 Pseudocode is written in the programmer’s native
language and concentrates on the logic in a program—
not the syntax of a programming language.
Pseudocode for a
Cash Register Program
sum=0
While More items do
Input price
sum=sum+price
End While
vat=sum x 0.25
total=sum+vat
Output sum, vat, total
Structured Programming
 Structured program languages lend themselves to
flowcharts and pseudocode.
 Structured programming languages work best
where the instructions have been broken up into
small, manageable parts.
Object Oriented Programming
 Everything is an object
 A program is a bunch of objects telling each
other what to do by sending messages
 Each object has its own memory made up of
other objects
 Every object has a type
 All objects of a particular type can receive the
same messages
(Alan Kay)
The object concept
 An object is an encapsulation of data and behaviour,
modeled after real-world objects
 An object is an instance of an abstract data type
 An abstract data type is implemented via a class
 An object has
 identity (a unique reference)
 state (also called characteristics)
 behaviour
 Behaviour is implemented via methods
 Methods are often implemented using structured programming
 An objects methods and state are access via dot notation
 I.e document.write(“Hello World”)
The Program Development Cycle
Analyze the problem
Design the solution algorithm
Design the user interface
Write the code
Test and debug the program
Complete the documentation
Programming and Debugging
 Write code
 Syntax

Rules of the language
 Logic

Order of execution of various parts of the program
Programming and Debugging
 Programming Errors
 Syntax error

Misuse of syntax
 e.g., typing fer instead of for
 Logic errors

Unintended operation of program
 e.g., Infinite loop
Programming and Debugging
 Debugging




Tracing and resolving errors in a program
Coined by Admiral Grace Hopper
 Moth short-circuited a relay
 “bug” in the system
 Removed it  system “debugged”
Not an exact science – more a black art
Human against evil machine!
So really, why learn about
programming?
 Programmers make lots of money.
 Programming really is fun.
 Programming is very intellectually rewarding.
 Programming makes you feel superior to other
people.
 Programming gives you complete control over an
innocent, vulnerable machine, which will do your
evil bidding with a loyalty not even your pet dog
can rival.