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Learning outcomes• Differentiate between variables and constants
• Differentiate between character, numeric and logical data
types
• ent y operators, operan s, an resu tants
• Identify and use operators according to their precedence
• Set up
and
evaluate
expressions
and
equations
• Understand and use pre‐defined functions
Six Basic
Computer
Operations1. A
computer
can
receive information
2. A computer can put out information
3. A computer can perform arithmetic
4. A compu er can ass gn a va ue o a var a e or memory location
5. A computer can compare two variables and select one
or two alternate actions
6. A computer can repeat a group of actions
1. A
Computer
can
receive Information
When a computer is required to receive information or input from a particular source, whether it is a terminal, a disk or any other device, the verbs Read and Get are used in
pseudocode.
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2. A computer can put out information
When a computer is required to supply information or output to a device, the verbs Print, Write, Put, Output, or Display are used in pseudocode
Usually an output Prompt instruction is required before an
input Get instruction
3. A Computer can perform arithmetic Most programs require the computer to perform some sort of
mathematical calculation, or formula, and for these, a
programmer may use either actual mathematical symbols or the words for those symbols
To be consistent with high‐level programming languages, the following symbols can be written in pseudocode:
+ for Add ‐ for Subtract
* for Multiply / for Divide
( ) for Parentheses
4. A computer can assign a value to a variable or memory location
There are three cases where you may write pseudocode to
assign a value to a variable or memory location:
1. To give data an initial value in pseudocode, the verbs Initializeor Set are used
2. To assign a value as a result of some processing the symbols ‘= is
written
3. To keep a variable for later use, the verbs Save or Store are used
5. A computer can compare two variables and select one or two alternate actions
An important computer operation available to the
programmer is the ability to compare two variables and then,
as a result of the com arison select one of two alternate
actions
To represent
this
operation
in
pseudocode,
special
keywords
are used: IF, THEN, and ELSE
6. A
computer
can
repeat a
group
of
actions
When there is a sequence of processing steps that need to be
repeated, two special keywords, DO,DOWHILE and
ENDDO, are used in pseudocode
The condition for the repetition of a group of actions is
established in the DOWHILE clause, and the actions to be
repeated are listed beneath it
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How we store data in a program?
Data within a program may be a single variable, such as an
integer or a character, or a group item (sometimes called an
aggrega e , suc as an array, s ruc ure, or a e
Data naming
convention
Name a variable according to what it represents (meaningful names)
Do not use spaces in a variable name
Start a variable with a letter
o not use any mat emat ca operator n var a e name
Be consistent when using upper and lower case characters.
Importance of Naming Convention Allows several programmers to work on the same
project without conflict in using variable’s name.
Allows program to be easily read due to consistency of variable’s name within a com an .
Code easily to maintain.
Software should perform more efficient.
Increase performance
expectation.
Produce clean, well‐ written program.
Example of Incorrect Variable Name
Data Item IncorrectVariable Name
Problem Correction
Hours worked hours worked Space betweenwords
hours_worked
Name of Client cn Does not definedata item
client_name
Rate of pay pay-rate Usingmathematicaloperator
pay_rate
Constants
• A constant is a data item with a name and a value that remain
the same (can never change) during the execution of the
program
• .g. const oat = 3.142xxx
• Any item whose value remains static during execution should
be defined as a constant
• const float govt_tax = 0.05 for Govt. Tax = 5%
• const float sales_tax = 0.1 for Sales Tax = 10%
• const float service_charge = 0.1 for Service Charge = 10%
Variables
• A variable is the name given to a collection of memory cells, designed to store a particular data item
• It is called a variable because the value stored in those memory cells may change or vary as the program executes
• E.g. total_sales = ????, (student_name = ????)• depends on amount of items bought …..
• Total amount, Total Bill, Total Discount, etc…
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Data Types
Data are unorganized facts
At the beginning of a program, the programmer must clearly define the form or type of data to be collected for the variables created
The data types can be
• Primitive Data Types, or
• Composite Data
1. Primitive Data Types
• An primitive data item is one containing a single variable
that is always treated as a unit
• A data t e consists of a set of data values and a set of
operations that can be performed on those values
• The most
common
elementary
data
types
are:
• integer * character * boolean
• float * double
2. Composite Types
• The data items that it contains are its components, which
may be primitive data items or another data structure
•
* Records * File (for permanent storage)
* Array * String
1. Data Type ‐ Numeric
• Numeric data
• Integers
• Real numbers
nteger : w o e num er, suc as 5297 or ‐3 7
can be positive or negative
Real number : also floating numbers ,
which are whole number plus
decimal part. e.g. 3.671234
2. Data Type – Character/Alphanumeric
• ALL single
digit
numbers,
letters,
and
special
characters
available in computer. (placed within quotation marks)
• E.g.: ‘A’, ‘a’, ‘1’, ‘@’, ‘#’, ‘+’
• Uppercase and lowercase considered different character
• Cannot be used for calculation
• ‘A’+ ‘1’ = ???
• One of more character can be combined into a “string”
• E.g. : “a”, “abc”, “Hello World 123 !!”
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3. Data Type – Logical/Boolean
• Have only two values – true or false
• Implementation in programming languages may differ
‘ ’ ‘ ’ ‘ ’ ‘ ’ • , , yes, no, 0, 1, e c
• Mainly used as a control flag or switch
• E.g.
• credit_ok = true
• cheque_cleared = “Y”
Rules for Data Types Most commonly used data types : numeric (integer and real
number), character(including character string), and
logical.
Pro rammer desi nates the data t e durin ro rammin
process
Use numeric data type for numeric item calculation. Other
numeric item
should
be
designated
in
character
or
character‐string data type even if data are all numbers, as in Zip Code
Data Validation
• Data should always undergo a validation check before it is processed by a program
• Different t es of data re uire different checks – for exam le:
* Correct type * Correct range
* Correct length * Completeness
* Correct date
Why
Input
Must
Be
Validated• Risk of data entry errors is high
• Large volume of data entered
• Human error keying in data
• Invalid input leads to inaccurate output• For example, salary reported incorrectly if entered as 23000 instead
of 32000
• Input error can cause program interrupt• For example, spaces entered for numeric field used in arithmetic
operation
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Operators Data connectors within expressions and equations.
Tell computer how to process data
What type of processing is to be done
Relational (to program decisions)
Logical to connect relational expressions to perform operations on logical data
Operators and Computer symbol
Mathematical Operator Result
Addition + 3 + 5 8
Relational Operator Result
Equal to = 5=6 FALSE
Less than < 5<7 TRUE
Greater than > 3>1 TRUE
Subtraction - 7.5 - 2 5.5
Multiplication * 4 * 2.5 10
Division / 60 / 3 20
modulo division % 13 / 7 5
Less thanor equal to <= 3<=3 TRUE
Greater thanor equal to >= 4>=7 FALSE
Not equal to != 5!=3 TRUE
Logical Operator Result
Not ! ! True FALSE
And && true AND false FALSE
Or || true OR false TRUE
Operator and Computer Symbol Example
int a = 5;
float b = 3.2;
a = + 6; (variable a will hold value = 11)
a = 5 % 2; (variable a will hold value = 1)
b = 5 / 2; (variable b will hold value = 2)
b+=3; ( b = b + 3)
a‐=2; (a = a ‐ 2)
Expressions and Equations
Expression An expression processes data (the operand) through the use
of operators
E.g. * eng w
Equation
An equation stores the result of an expression in a memory location through the equal (=) sign the assignment operator
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Setting Up Expression and Equation
X+6
X(3Y+4) – 4Y
Y + 3 is equal to X(Z + 5)
X is less than Y + 5
Evaluating Mathematical Expression
Let’s say X = 2, Y = 3, Z = 6
5 * (X + Y) – 4 * Y/(Z+6)
Y + 3 == X * (Z + 5)
X < (Y + 5)
Evaluating a Logical Expression
Example: A AND B OR C AND A
A=True B=False C=True
Operation Resultant
1. A AND B False
2. C AND A True
3. Resultant of 1 ORresultant of 2
True
Function
Function is a block of program statement that will perform
specific task and in some of the case, return the results to
the program.
There are several rules about function in C program1) Every C program consist of one or more functions
2) One of them must be named main
3) Program will start and end with the main function
4) main function is the “boss” of all functions, if there is any additional functions, they are subordinate to main.
5) main can call other function to do some tasks.
Function Q: Why we need to have several functions in a program?
A: There are actually many reasons for creating more than
one functions in a program, as we learn along, you will know the reasons behind this. But for the moment ust tr
to imagine, is it better to have one person to do all the job?
Or have several people to split the job?
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Function Creating different functions in a program is like having
different departments in a company.
In real life, a company will have different departments, each de artment is s ecialize in erformin certain task.
E.g. HR department handle the employees related task, Finance department handle the company funds.
In programming, each function is specially designed to
solve different problem.
Types of Function Predefined Function
Usually built in with the compiler
Written by the developer to solve some common task
Self ‐defined Function (chapter 4)
In most of the situation, we can’t solve all the problem
by using pre‐defined function. We need to write our own function.
A customized instructions that written by ourselves are
known as Self ‐defined Function
Predefined Function Mathematical functions.
Contains most of the science, business and mathematical functions such as square root, random numbers and power.
String functions.
Used to
manipulate
string,
for
example
copy
part
of
the
string
into another variable, find the length or the number of characters in the string.
Predefined Function Conversion functions.
Used to convert data from one data type to another .
.
Used to calculate things such as maximum values, minimum
values, and so forth.
Utility functions.
Used to access information outside the program and the language in the computer system such as include date and
time functions.
Summary 6 basic computer operations
Constants and Variables
Data types
Operators
Expressions and Equations