Transcript ProgFunda1 - University of Florida

CIS3023: Programming Fundamentals for CIS Majors II
Introduction to Problem Solving, Algorithms and Pseudocode,
Programming in JAVA - I
Course Lecture Slides
Summer 2010
Ganesh Viswanathan
Announcements
• CISE systems are being upgraded. CISE
webpages were down yesterday!
• So, course slides will also be posted on
E-Learning (http://lss.at.ufl.edu) from now on.
• E-Learning contains course schedule and
weekly schedule.
• Midterm: June 14
Final Exam: Aug 5
Location: TBA
Problem Solving
Using a step-by-step programmatic approach to find a
solution for complex problems
Image credits: coventry.gov.uk
Problem-Solving Model
Iterative Process!
Image credits: usf.edu
Problem 1
Give a rough estimate of the number of cellphones in
the University of Florida Gainesville campus.
How to become a better problem
solver
- Break the problem into parts
- Actively work to check your understanding
- Recognize limitations and pitfalls
- Be open, Engage confusing problems,
Brainstorm ideas, and Learn techniques that
you can apply in a wide range of scenarios.
Problem 2
If the triangle below is shorter than the square and the circle is taller
than the square, then label the triangle “1”. However, if this is not the
case, label the second tallest figure as “2”.
Problem-Solving Model
1. Define the problem
2. Analyze and decide course of action
(design algorithm)
3. Plan solution and verify goals
4. Generate solutions
5. Testing and Evaluation
Iterative Process!
Algorithm
What is an algorithm?
An algorithm is an effective procedure for solving
a problem expressed as a finite sequence of
instructions.
“effective procedure” = program
Problem = set of instances of a question
Solution = set of answers to these instances
Algorithm
What is an algorithm?
An algorithm is an effective procedure for solving
a problem expressed as a finite sequence of
instructions.
e.g., PRIME numbers
Is 2 a prime?
Is 3 a prime?
Is
10500
a prime?
Is
6
24
810
a prime?
Algorithm
What is an algorithm?
An algorithm is an effective procedure for solving
a problem expressed as a finite sequence of
instructions.
Problem = question + input parameter(s)
The size of a problem can be characterized by an integer n
PRIME: #digits of input parameter
SORTING: #inputs
Algorithm
Is there an algorithm for each problem?
NO!
1. The problem (question) needs to be effectively specified.
“How many angels can dance on the head of a pin” is not an
effectively specified problem.
2. Even it effectively specified, there is not necessarily an
algorithm to solve every problem.
Algorithm
ULAM’s Problem:
Given f(n) = if n=1 then stop else
if n is even then f(n/2)
else f(3n+1)
Question: Will f(n) stop ?
f(1) Stop
f(2) → 1 → stop
f(3) → 10 → 5 → 16 → 8 → 4 → 2 → 1 → stop
f(4) → 2 → 1 → stop
f(5) → 16 → 8 → 4 → 2 → 1 → stop
f(6) → 3 → (etc., as for 3 above) → stop
f(7) → 22 → 11 → 34 → 17 → 52 → 26 → 13 → 40 → 20 → 10 → 5 → … → stop
• Nobody has ever found an n for which f doesn’t stop !!
• Nobody has ever found a proof that f stops for all natural numbers (n>0) !!
Algorithm
Q: Search for a value in an array of numbers.
i
1
2
3
4
5
6
A
100
20
50
80
10
90
LINEAR-SEARCH [A, n, x]: Searches the array using basic linear search to find
a match for x.
INPUT: Unsorted array A of n natural numbers. Search key x.
OUTPUT: If search key is found, returns its location in the array, else “x not found”
1 for i ← 1 to n
2
do if A[i] = x
3
then return i
4
else i ← i + 1
5 return “x not found”
Pseudocode
• A compact and informal description of algorithms using the structural
conventions of a programming language and meant for human reading.
• A text-based design tool that helps programmers to develop algorithms.
Q: Write a pesudocode to print pass/ fail for each student based
on grade. Pass is 60 points or higher.
A: //Pseudocode to print student pass/fail status.
If student grade > 60
print “pass”
Else
print “fail”
Pseudocode
Q: Write a pesudocode to compute the class average for upto n
students in Exam1, from user input.
A: //Pseudocode to compute class average for n students
Set average = 0, total = 0, grade = 0
Set grade counter = 0
While user has entered a grade
While (grade counter) < n
Input next grade
Add grade to total
Increment grade counter
If grade counter != 0
Set average = ( total / n )
Print “class average is “ average
Always remember to
test-run your pesudocode
to check for correctness.
JAVA
Who is this guy?
James Gosling
- “invented” JAVA in 1994 !!
JAVA
Java 1.0 was first released by
Sun Microsystems in 1995.
Java became popular for web programming.
"Write Once, Run Anywhere" (WORA) philosophy.
Key design principles:
- Platform independence
- Security
- Stability
Duke, the
JAVA mascot
How Java works!
Programming in JAVA – I
Basic concepts in Java
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Values
Variables
Complex data/objects
Functions/methods
Expressions
Conditionals
Loops
Programming in JAVA
English to JAVA translation:
•
•
•
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Piece of data: value
Kind of data: type
Place to store a value: variable
Structured group of variables: object
Kind of object: class
Object of a particular class: class instance
Variable belonging to an object: instance variable
Programming in JAVA
Values and Types:
• All data values in Java have a type
• The type of a value determines:
• Allowed operations
• Memory representation
• Allowed operations
• Conversion to other types
• Allowed operations
• Types are program invariants
• Help to catch errors
Default initial values
(if omitted) are based
on type
Programming in JAVA
Primitive Types:
• EIGHT basic pre-defined types: values on
which Java can operate directly.
• byte, short, int, long, float, double,
boolean, char
• Plus, special support for character strings
- using java.lang.String class