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Programming Constructs
Andrew Csizmadia
Monday 5th December 2016
Prerequisites for Learners
• For learners to be successful in using and
engaging with programming theory, they will
need to be:
– Familiar with fundamental programming constructs:
selection, sequence and iteration
– Able to successfully read pseudocode
– Able to successfully write pseudocode
– Able to successfully debug pseudocode
– Able to use successfully use Computational Thinking
concepts
ARRAYS
Simple vs Structured Data Types
• Simple data type => data element contains a
single value
x : 15
avg : 84.35
ch : ‘A’
• Structured data type => a data element
contains a collection of data values
scores : 85 79 92 57 68 80
name : ‘C’ ‘L’ ‘Y’ ‘D’ ‘E’
4
Big Idea - Array
• A variable can have a value that combines
many values.
• You can:
– Extract one value
– Update part of the variable
• This idea is essential for representing complex
data in programs:
– a song,
– an image
– a map
Big Idea - Arrays
• An array is a static data structure,
– i.e. its size is fixed
• Can:
– Select (i.e. index) one entry
– Update one entry
• Cannot:
– Add an extra entry to the start or end
– Insert/remove item from the middle
Arrays
• Arrays are Structured Static Data Types
• They have a means of accessing individual
components using an index
• Values can be retrieved from and stored in the
structure
Structure given a single name
0
Votes
1 2 3
Index
12
4 5
0
34
23
43
21
35
22
1
2
3
4
5
6
Individual elements accessed by index (integer Value) indicating relative
position in collection
Arrays (1D) - Overview
• Structure - List
• Techniques - Create, Initialise, Search, Sort, Find
Item, Reverse
• Implementation:
– Python (List)
• Application(s):
– Searching (Linear, Binary)
– Sorting (i.e. Quicksort)
Two-Dimensional (2D) Arrays
• Arrays may have multiple dimensions.
• Two-dimensional arrays can be visualized as tables
with rows and columns.
• A two dimensional array is really an “array of arrays”
where each element of a one-dimensional array
contains another array.
Declaring a 2D Array
Here is how you would
declare a two-dimensional
array chessboard with 8
rows and 8 columns:
0
1
R
o
w
s
2
chessboard = table[8] [8]
3
chessboard = table[8, 8]
4
5
chessboard[8][8]
6
chessboard[8, 8]
7
0
1
2
3
4
Columns
5
6
7
Which Way to label?
Which way should be label/reference a two dimensional array?
R
o
w
s
0
7
1
6
2
OR
3
4
5
6
7
R
o
w
s
5
4
3
2
1
0
0
1
2
3
4
5
Columns
6
7
0
1
2
3
4
5
Columns
Which square is Chessboard [4, 4] is referring to?
6
7
Conceptualizing Two-D Arrays
int [ ] [ ] table = new int [4][5];
The variable table references an array of four elements.
Each of these elements in turn references an array of five integers …
table is really an array of arrays.
Conceptualizing Two-D Arrays
More specifically, table is an array of four memory locations and in each
memory location of that array there is an array that has five memory
locations. So table[0] refers to the first row of the 2D array and table[1]
refers to the second row, table[2] refers to the third row and table[3] refers
to the fourth row.
Using the code table[2][3] allows us to work with the memory location in
the third row and fourth column named row 2 column 3.
Conceptualizing Two-D Arrays
A table of numbers, for instance, can be implemented
as a two-dimensional array. The figure shows a
two-dimensional array with four rows and five
columns that contains some numbers.
Accessing an Element of a Two-D Array
Suppose we name the array table; then to indicate an
element in table, we specify its row and column
position, remembering that index values start at 0:
x = table[2][3];
// Set x to 23, the value in (row 2, column 3)
Arrays (2D) - Overview
• Structure - Table
• Techniques - Create, Initialise, Search, Sort, Find Item,
Reverse
• Implementation:
– Python (List of lists)
• Application(s):
–
–
–
–
–
Storing a table of data
Image representation
Game simulation
Modelling relationships, networks and maps with graphs
Building blocks for other data structures, i.e. trees
RECORDS
Records
• In computer science, a record :
– contains a collection of data for each entity
– usually recorded as a row in a table
SQL (STRUCTURED QUERY LANGUAGE)
SQL (Structured Query Language)
• SQL stands for Structured Query Language.
• It is the most commonly used relational
database language today.
• SQL works with a variety of different fourthgeneration (4GL) programming languages, such
as Visual Basic, Python.
SQL is used for:
•
•
•
•
Data Manipulation
Data Definition
Data Administration
All are expressed as an SQL statement or
command.
SQL Requirements
• SQL Must be embedded in a programming
language, or used with a 4GL like VB or Python
• SQL is a free form language so there is no limit
to the number of words per line or fixed line
break.
Not all versions are case sensitive!
• Syntax statements, words or phrases are always
in lower case; keywords are in uppercase.
SQL and Relational Database
A Fully Relational Database Management System must:
• Represent all info in database as tables
• Keep logical representation of data independent from its physical storage
characteristics
• Use one high-level language for structuring, querying, and changing info
in the database
• Support the main relational operations
• Support alternate ways of looking at data in tables
• Provide a method for differentiating between unknown values and nulls
(zero or blank)
• Support Mechanisms for integrity, authorization, transactions, and
recovery
Design
• SQL represents all information in the form of
tables
• Supports three relational operations:
selection, projection, and join.
• These are for specifying exactly what data
you want to display or use
• SQL is used for data manipulation, definition
and administration
Table Design
Columns describe one
characteristic of the entity
Name
Address
Jane Doe
123 Main Street
John Smith
456 Second Street
Mary Poe
789 Third Ave
Rows describe
the Occurrence
of an Entity
Data Retrieval (Queries)
• Queries search the database, fetch info,
and display it. This is done using the
keyword SELECT
SELECT * FROM publishers
pub_id
pub_name
address
state
0736
New Age Books
1 1st Street
MA
0987
Binnet & Hardley
2 2nd Street
DC
1120
Algodata Infosys
3 3rd Street
CA
The Operator asks for every column in
the table.
*
Data Retrieval (Queries)
• Queries can be more specific with a few
more lines
SELECT *
from publishers
where state = ‘CA’
pub_id
pub_name
address
state
0736
New Age Books
1 1st Street
MA
0987
Binnet & Hardley
2 2nd Street
DC
1120
Algodata Infosys
3 3rd Street
CA
Only publishers in CA are displayed
Data Input
• Putting data into a table is accomplished
INSERT
using the keyword
Variable
INSERT INTO publishers
VALUES (‘0010’, ‘pragmatics’, ‘4 4th Ln’, ‘chicago’, ‘il’)
Keyword
pub_id
pub_name
address
state
0736
0010
New Age Books
Pragmatics
st Street
11
4
4th
Ln
MA
IL
0987
0736
Binnet
& Hardley
New
Age
Books
nd Street
21
2st
Street
1
DC
MA
1120
0987
Algodata
Infosys
Binnet
& Hardley
rd Street
32
3nd
2
Street
CA
DC
1120
Algodata Infosys
3 3rd Street
CA
Table is updated with new information
Types of Tables
There are two types of tables which make up a relational database in SQL
• User Tables: contain information that is
the database management system
• System Tables: contain the database
description, kept up to date by DBMS
itself
Relation
Table
Tuple
Row
Attribute
Column
Using SQL
SQL statements can be embedded into a program (cgi or
perl script, Visual Basic, MS Access)
OR
SQL statements can be entered directly at the
command prompt of the SQL software being used
(such as mySQL)
Using SQL
To begin, you must first CREATE a database using the
following SQL statement:
CREATE DATABASE database_name
Depending on the version of SQL being used the
following statement is needed to begin using the
database:
USE database_name
Using SQL
• To create a table in the current database,
use the CREATE TABLE keyword
CREATE TABLE authors
(auth_id int(9) not null,
auth_name char(40) not null)
auth_id
auth_name
(9 digit int)
(40 char string)
Using SQL
• To insert data in the current table, use the
keyword INSERT INTO
INSERT INTO authors
values(‘000000001’, ‘John Smith’)
Then issue the statement
SELECT * FROM authors
auth_id
auth_name
000000001
John Smith
Using SQL
If you only want to display the author’s name and city from the following
table:
auth_id
auth_name
auth_city
auth_state
123456789 Jane Doe
Dearborn
MI
000000001 John Smith
Taylor
MI
SELECT auth_name, auth_city
FROM publishers
auth_name
auth_city
Jane Doe
Dearborn
John Smith
Taylor
Using SQL
To delete data from a table, use the DELETE statement:
DELETE from authors
WHERE auth_name=‘John Smith’
auth_id
auth_name
auth_city
auth_state
123456789 Jane Doe
Dearborn
MI
000000001 John Smith
Taylor
MI
Using SQL
To Update information in a database use the UPDATE keyword
UPDATE authors
SET auth_name=‘hello’
auth_id
auth_name
auth_city
auth_state
Hello Doe
123456789 Jane
Dearborn
MI
Hello Smith
000000001 John
Taylor
MI
Sets all auth_name fields to hello
Using SQL
To change a table in a database use ALTER TABLE. ADD adds a characteristic.
ALTER TABLE authors
ADD birth_date datetime null
auth_id
auth_name
Type
Initializer
auth_city
auth_state
birth_date
123456789 Jane Doe
Dearborn
MI
.
000000001 John Smith
Taylor
MI
.
ADD puts a new column in the table called birth_date
Using SQL
To delete a column or row, use the keyword DROP
ALTER TABLE authors
DROP birth_date
auth_id
auth_name
auth_city
auth_state
auth_state
123456789 Jane Doe
Dearborn
MI
.
000000001 John Smith
Taylor
MI
.
DROP removed the birth_date characteristic from the table
Using SQL
The DROP statement is also used to delete an entire database.
DROP DATABASE authors
auth_id
auth_name
auth_city
auth_state
123456789 Jane Doe
Dearborn
MI
000000001 John Smith
Taylor
MI
DROP removed the database and returned the memory to system
Time Left:
Activity: w3Schools’ SQL Tutorial
Work through w3Schools’ SQL tutorial
SQL
Learning Mat
SQL
Workbook
SC : Creating and Manipulating SQL Databases
Challenge
Time Left:
Activity: SQL with Khan Academy
Work through Creating SQL
databases with Khan Academy
SQL
Learning Mat
SQL
Workbook
SC : Creating and Manipulating SQL Databases
Challenge
Time Left:
Activity: SQL with Access
Explore using SQL with Northwest
Trader
SQL
Learning Mat
SQL
Workbook
SC : Using SQL with Access
Challenge
SQL Summary
• SQL is a versatile language that can
integrate with numerous 4GL languages
and applications
• SQL simplifies data manipulation by
reducing the amount of code required.
• More reliable than creating a database
using files with linked-list implementation
Design - Subroutines
• Subroutines are used to
allows us to breakdown
(decompose) a complex
task into a set of solvable
tasks in order to produce
a solution to the original
task.
• Subroutine may be :
– a function which returns
value(s)
– a procedure which does
not return a value
Design - Subroutines
• Using subroutines allows
the designer or
programmer to focus on
one task as a time.
• Advantages
– Modular approach
– Efficient – only need to
replace subroutine if
change is required.
Subroutines and Parameters
move (playerToPlay)
----------------------------------------------------------------------------------------------------------
① currentPlayer = playerOne
move(currentPlayer)
currentPlayer = playerTwo
move(currentPlayer)
③
②
④
• Value(s) can be passed
to a subroutine via
parameter(s) to be used
in that subroutine
• Aim – create a
generalised subroutine,
which perform the same
task using different
values. (Efficient design,
Elegant design).
Time Left:
Task : Tic-Tac-Toe Design
Identify the subroutines that would be
used to design a program to play tictac-toe (O-X-O)
Challenge(s)
Identify the
subroutines
which will
need
parameter(s)
passed to
them
Identify the
subroutines
(functions)
which will
return
parameter(s)
SC : Identify the subroutines requited to play Tic-Tac-Toc (O-X-O)
Any questions?