Transcript Algorithm-Program - School of Information Technology

Concepts of Programming Languages
TK 327, Fall 2015
MW 2:00 PM – 3:15 PM
STV 104
Instructor: Dr. Chung-Chih Li
Home page of the Class
1
Concepts of Programming Languages
This is not a survey course
• Course Description and Purposes
• Objectives
2
In order to understand the universe,
we have to understand the language in which
the universe is written,
and mathematics is the language.
-- Galileo Galilei (1564 -1642) --
In order to understand Information Technology,
we have to understand the language in which
Information Technology is written,
and the Programming Language is the language.
-4/2/2016
-ITK 327
3
What is a computer?
A machine that can compute!
What is a machine?
What is computation?
Why bother?
Because, the way we understand and
formalize them directly shapes the design of
programming languages.
4
Computer -A machine that can compute!
Machine -A device that follows a certain fixed
causal rules.
Computation -A sequence of procedures that
manipulate data.
5
design:
Difference Engine No. 1 (1821-1832)
Analytical Engine
(1834-1840)
Difference Engine No. 2 (1840-1849)
http://www.computerhistory.org/babbage/
Charles Babbage (1791-1871)
Difference Engine No. 2
(2002)
Difference Engine No. 1
4/2/2016
6
Gottfried W.V. Leibniz
(1646-1716)
Leibniz’s Dream
“Sir! Let’s sit down and
compute!! ”
http://sunsite.informatik.rwth-aachen.de/phil/filosofer/leibniz.html
7
Logic and Thought and Computing
Aristotle (384 - 322 BC)
L E J Brouwer (1881-1966)
http://www.klima-luft.de/steinicke/ngcic/persons/aristoteles.htm
8
Completeness theorem
Incompleteness theorem
Recursive theory
Computable functions are
recursively definable
function
Kurt Gödel
(1906-1978)
http://www-groups.dcs.st-and.ac.uk/~history/PictDisplay/Godel.html
9
Alonzo Church
1903-1995
Lambda Calculus
Computable functions are
Lambda-term definable
http://www.princeton.edu/pr/pwb/03/0505/7a.shtml
10
Alan Turing (1912-1954)
– The Enigma
The man who invented the
computer.
Computable functions are
Turing machine computable
Image from http://ei.cs.vt.edu/~history/Turing.html
11
Ludwig Wittgenstein (1889-1951)
Wittgenstein says:
“Turing Machines are
human that compute.”
http://www.ags.uci.edu/~bcarver/wgallery.html
12
Church-Turing Thesis: all algorithms are computable
1. Logic
Logical languages
e.g. PROLOG
2. Recursive, λ-terms
Functional languages
e.g. LISP, ML
3. Turing machines
Imperative languages
e.g. Algol-60, Fortran, C
?????
OOP, (e.g. Small Talk, JAVA, C++)
What is it? Really?
13
Imperative Languages
• C
int fact(int n) {
int sofar = 1;
while (n>0) sofar *= n--;
return sofar;
}
Using instructions to command the machine to
do something, with branches, iterations, control
flows, and side-effects,.
14
Functional Languages
• ML
fun fact x =
if x <= 0 then 1 else x * fact(x-1);
• LISP
defun fact (x)
(if (<= x 0) 1 (* x (fact (- x 1)))))
Function definition, Recursion, no side-effect
15
Logical Languages
grandparent(X, sean).
X = john.
• PROLOG
parent(A,B) :parent(A,B) :-
dad(A,B).
mom(A,B).
grandparent(A,B) :parent(A,C), parent(C,B).
parent(X, leon).
X = dennis.
X = sandy.
dad(dennis, sean).
dad(dennis, leon).
dad(john, dennis).
mom(sandy, leon).
Rules (logic) and facts
mom(sandy,sean).
16
Logical Languages
• PROLOG
fact(X,1) :X =:= 1.
fact(X,Fact) :X > 1,
NewX is X - 1,
fact(NewX,NF),
Fact is X * NF.
fact(4,X).
X = 24.
fact(5,30).
false.
17
OOP (Object-oriented Programming)
A new programming paradigm after ’80s.
Problem solving  Procedure finding
But
Why should I have to write the same procedure to
do the same job over and over again?
Fact:
Different problems usually consist of many
common smaller problems.
Problem solving  Solution arranging
18
OOP
• Java
public class MyInt {
private int value;
public MyInt(int value) {
this.value = value;
}
public int getValue() {
return value;
}
public MyInt getFact() {
return new MyInt(fact(value));
}
private int fact(int n) {
int sofar = 1;
while (n > 1) sofar *= n--;
return sofar;
}
}
19