PROGRAMMING LOGIC
GWDA123
Sharon Kaitner, M.Ed.
Winter 2015: Week 1
Week 1
1
• Computer Components
and Operations
2
• Planning Logic
3
• Pseudo Statements
4
• Variables
5
• Data types
6
• Keywords
Learning Objectives
• Explain how scripts
are included,
handled and
processed by
browsers
Computer components & operations
• Your computer is composed of the
hardware, or computer equipment, and
the software, the instructions that tells the
hardware what to do
• Software programs are instructions
written by programmers
Computer components & operations
• Generally, there are two types of software:
– Application or task software like Word or PhotoShop
– System software, the programs that manage your
computer like your operating system of Windows
• We will focus on the logic in writing application
programs. The instructions you will write is
called program code.
Computer components & operations
• Computers perform 3 major operations
– Input – keyboard and mice entry of data
– Processing – Organizing, checking, perhaps
performing mathematical operations, on the data,
performed by the central processing unit or CPU
– Output – the bits of entered data is processed into
information, usable by people to see, interpret and
use via a monitor, printer, or other output device
Computer components & operations
• Our software instructions are written in a
programming language, such as Java or C+
• Rules for writing is called the syntax
• Computers need you to be exact when you
write instructions
• If the syntax isn’t perfect, the computer
won’t understand
Computer components & operations
• Computers operate on circuitry that consists of
millions of on/off switches
• Each programming language uses a piece of
software to translate your statements into object
code, or machine language
• Machine language is a series of 0s and 1s, called
binary form
Computer components & operations
• The software that translates your statements
into binary form is called a compiler or
interpreter
• It will issue a message warning if you had made a
syntax error, such as misspelled a word or used
incorrect punctuation
• Syntax errors are relatively easy to find and fix
Computer components & operations
• The compiler highlights the errors and your
program will not run until the error is fixed
• There are different compilers and interpreters
but generally their function is to translate your
programming statements into code the
computer can understand
• The program runs and executes a program’s
instructions
Computer components & operations
• If there are no syntax errors, the program will
run
• However, it may still not give correct information
Computer components & operations
• To work right, the instructions need to go to the
computer in a specific sequence
• No instruction can be left out
• You may not add extraneous instructions
• …in other words, you develop the logic of the
computer program
Computer components & operations
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Stir
Add two eggs
Add a gallon of gasoline
Bake at 350 degrees for 45 minutes
Add three cups flour
Computer components & operations
• Though the instructions were written in correct
English spelling and grammar, the instructions
were out of sequence, some instructions were
missing, and some instructions belonged to a
different procedure.
• These are logical errors, and they are more
difficult to find than syntax errors.
Computer components & operations
• While compilers stop at a syntax error until it is
fixed, errors in logic cannot be as easily located
by the compiler. It usually needs to execute the
program before errors can be found.
• Logic is the same across all the different
languages you can write
Computer components & operations
• Write a program that takes a number (input)
• Double it (processing)
• Tell the answer (output)
• Input originalNumber.
• Compute calculatedAnswer = originalNumber
times 2.
• Output calculatedAnswer.
Computer components & operations
• Input originalNumber is an example of an input
operation.
• The computer knows to interpret the
instructions using an input device to obtain a
number and store it in memory named
originalNumber
• You would tell the computer what input device
to use, but by default it’s the keyboard
• These are processing steps
Programming process
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Understanding the problem
Plan the logic
Code the program
Translate the program into machine language
Test the program
Put program into production
Maintain the program
Programming process
• Understanding the problem
– Give me a list of students who are over 25 years of
age with 25 or more college credits
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All students, AI students, currently attending?
25 years of age to no limit?
Credits earned at this college?
How does the information need to be delivered?
What data is currently available?
?????
Programming process
• Plan the logic
– Plan the steps of your program, decide what actions
to include and their order
– Called developing an algorithm
– Algorithm is a sequence of steps to solve a problem
– Flowcharts and pseudocode are common planning
tools to plan and show all necessary steps
– Writing out the steps on paper is called desk-checking
Programming process
• Code the program
– After the developing the logic, a language is chosen to
handle the type of operation the programmer wants
– Then using the correct syntax can be employed
– The prior planning step is actually more difficult than
writing correct syntax code since now you are
translating
– There are many programming languages, but
computers only understand one: machine language
Programming process
• Code the program
– Machine language is understood by the computer
because the computer is made of the same system of
1s and 0s, thousands of tiny electrical switches turned
on (1) and off (0) state
– Languages like Java are used because someone wrote
a translator (compiler or interpreter) program that
turns the high-level programming language into lowlevel machine language
Programming process
• Code the program
– Writing your program with misspelled, missing or
“illegal” grammar will cause the translator program to
issue an error message identifying a syntax error
– It will not execute a program that contains even one
syntax error
Programming process
• Code the program
– Usually you will write some code and then submit it,
troubleshoot any errors, and repeat
– An executable program is created only when there
are no syntax errors
Programming process
• Test the program
– No syntax errors does NOT mean no logical errors
– When the program is syntax error free, the
programmer executes the program with some sample
data to find if results are logically correct
– If not, maybe the program has logic errors that need
to be corrected
– Programs should be tested with many sets of data
Programming process
• Put program into production
– Upon completing the production and testing of a
program, it is put into use
– If it is a simple program like providing a list, it might
just be ran once as needed
– If it is a large company-wide program, there may be
months or years of feedback and training as a
conversion to the new program occurs
Programming process
• Maintain the program
– Maintenance involves updating the program as
needed after it is put into use
– Writing clear code, commenting your steps, using
reasonable identifiers for values, and documentation
will all make this process easier for you or whoever
takes over the program implementation
Pseudocode statements & flowchart symbols
• Pseudocode is an English-like listing of the logical
steps it would take to solve a problem. It means
false code
• A flowchart is the pictorial representation of the
same thing
start
input originalNumber
compute calculatedAnswer as originalNumber times 2
output calculatedAnswer
stop
Pseudocode statements & flowchart symbols
• A flowchart is the pictorial representation of the
same thing
start
input originalNumber
compute calculatedAnswer as originalNumber times 2
output calculatedAnswer
stop
Pseudocode statements & flowchart symbols
Programmers usually use either pseudocode
or a flowchart, not usually both. Pseudocode
is similar to step by step instructions, while a
flowchart is like a map
LAB: VARIABLES
AND DATA TYPES
Using and naming variables
• We ask the computer to store our program in
variables
• Variables are named memory locations
• originalNumber is stored in a location as a
variable, and its content can vary
• One memory location can be used many
times, with different values
Using and naming variables
• You can write program instructions once but
use for thousands of separate calculations
• This is what makes programming valuable
• The ability of memory variables to change in
value makes computers and programming
valuable
Using and naming variables
• A variable name is called an identifier
• Each programming language has its own set
of rules for creating identifiers
• Most allow bot letters and digits
• Some allow hyphens (-), while others allow
underscores (_). Some do not allow either.
Using and naming variables
• Some languages, like php, allow dollar ($)
signs, and others foreign alphabet characters
• Different languages put different limits on the
length of variables but in general, newer
languages allow longer names
Using and naming variables
• Newest versions of C++, C#, and Java, allow
almost unlimited identifier names
• These languages are case sensitive
• Camel casing is when programmers use an
uppercase letter for the second word, like
hourlyWage
• Pascal casing is when the first letter is
uppercase, as in HourlyWage
Using and naming variables
• Logic works with any language so there are
only two rules when naming a variable:
– Variable names must be one word
– Variable names must have meaning
• The first is a rule: no programming language
allows spaces with a name. The second is a
best practice, making your logic more useful
Assigning value to variables
• Assignment statements involve two actions:
– The computer calculates the arithmetic value
– The computed value is stored in memory
• In pseudocode this could be written as:
Compute calculatedAnswer as originalNumber times 2
• An assignment statement would be written like this:
calculatedAnswer = originalNumber * 2
• The assignment operator is the equal (=) sign
• = means assignment not equivalency
Named constants
• Most programming languages allow creating named
constants
• You would use a constant when you want a value that
doesn’t change
• Unlike a variable, a constant would not have different values
over time
• Giving an appropriate name in uppercase and underscores is
naming the constant, instead of leaving unnamed (called a
magic number) that maybe isn’t apparent
Named constants
• Example: If a program needs the sales tax included, you
could declare the named constant:
num SALES_TAX = 0.06
Then write the program statement:
finalPrice = price + price * SALES_TAX
• Named constants are declared differently among
programming languages. We are using a standard
convention
Arithmatic operations
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+ (plus sign) addition
- (minus sign) subtraction
* (asterisk) multiplication
/ (slash) division
Most modern languages also include a remainder operator,
represented by a percent sign (%), to represent a remainder
after a division operation
Arithmetic operations
• You can combine arithmetic statements, each operator
following rules of precedence
• Rules of precedence dictates the order the operations are
carried out
• Multiplication and division always takes precedence over
addition and subtraction.
a+b*c
In this expression, you would multiply b and c, then add a
Arithmetic operations
• In arithmetic statements, the rules of precedence can be
overridden by using parentheses
2+3*4
(2 + 3) * 4
rules of precedence says the answer is 14
using parentheses gives 20 as the answer
• Forgetting to add parenthesis or the rules of precedence can lead to
logical errors hard to find in a program when you’re troubleshooting
• Choose to use parenthesis to help make your intention clear as needed
Data types and declaring variables
• Computers use two basic types of data
– Numeric with a specific numeric value called a
numeric constant. 43 is always 43 and you write
using the digits, no quotation marks
– A string constant, or text, is enclosed within
quotation marks, unnamed and literal “Amanda”
Data types and declaring variables
• A variable’s data type describes kind of value
– A numeric variable can have math operations
performed on it
– A string variable can hold alphabet and special
characters like punctuation marks. It is text
• Computers handle the two types differently, so you’re
distinguishing the two when you declare the variable
Data types and declaring variables
• When you declare the variable you let the
computer know the data type and an identifier to
expect
• You must declare the variable first
string lastName
num salary
• then you can assign value, send to output, or perform an
operation allowed for its data type
Data types and declaring variables
• You add a sentinel value to end a program, to
prevent situations like an infinite loop
• Computers are binary so you could give a dummy
value that is not real data but signals stop, and in a
flowchart, would be represented by a decision
symbol shaped like a diamond
• There would be only two mutually exclusive
answers, yes or no, true or false
Data types and declaring variables
• originalNumber = 0? for “Is the value of originalNumber
equal to 0?”
• Many programming languages use the term eof for “end of
file” to refer to a marker automatically stored at the end of
data
• This acts as a more efficient sentinel value
Case Study
• Create the logic for a Mad
Lib program that displays a
message asking the user to
provide five words
And then accepts those words and creates and displays
a short story or nursery rhyme using them
Require two nouns, an adjective, and a past-tense verb
Discussion
• What are you going to
use, pseudocode or
flowchart?
• What data type?
• What are the sequence
of steps?
• How would you signify
the sentinel value?
Homework Assignment
• Develop the logic for your favorite recipe.
Due the night before the next class, in the
dropbox for week 1