chapter 2 updated - color

7/27/2019 Chapter 2 Updated - Color

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10/15/2013

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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

chapter 2 updated - color

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