Slide 04 - Variables and Constants

8/10/2019 Slide 04 - Variables and Constants

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Computer Science Department FTSM

Variables and Constants

Knowledge:

Understand the concept of storage location representation asidentifiers

Skill:

Identify and define data types in C programs


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TK1913-C Programming 2

IntroductionConsider the following example:

#include

void main() {

printf(Welcome to UKM\n);

}

Lets recap

Which one is the preprocessor

instruction?

Which one is the main

function?


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C Program Structure

Preprocessor

Instruction

Pengisytiharan globl

void main (void)

{

}

Pengisytiharan setempat

Statement

Global Declaration

Local Declaration

Still rememberthis diagram?


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Identifiers

Identifiers are:

Variable

Constant

Function

Others


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Identifiers

Syntax Rules:

Consist of only letters, digits and underscores

Cannot begin with a digit

Cannot use C reserved words

Try not to use/redefine C standard identifiers

What are C

reserved words?

What are C standard

identifiers?


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C Reserved Word

A word that has special meaning in C

C Standard Identifier

A word having special meaning but may beredefined (but is not recommended!!)

Examples of reserved word:

int, void, double, returnExamples of standard identifiers:

printf, scanf

Identifiers


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Variable

A name associated with a memory

cell whose value can change

Needs to be declared:

variable_type variable_name;

Example:int x;

int entry_time, charge;


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VariableTypes of variable:

Character: char

An individual character valuea letter, a digit or a

symbol (e.g. A, 4, *) Integer: int

Whole numbers (e.g. +16, 568, -456)

Float: float

A real number which has a decimal point (e.g. 8.00,

3.1416)

High-level Float: double


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Variable

Variable Declaration:

Example 1:

char letter;

letteris a character-type variable

Example 2:

float matric;

matricis a ??? variable


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Variable

Example:

Calculate and display the price of a number of

apples if the quantity in kg and price per kg aregiven.

Input: quantityand price_per_kg

Output: price

Process: price= quantity* price_per_kg


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Variable

Example:

int quantity;

float price_per_kg;

float price;

Why did we

declare it as int?

Why did wedeclare them as

float?


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Example:

int number1, number2;

number1 = 25;

number2 = 23;

number1 = number2;

Variable - Value Assignment

number1 ?

number2 ?

2523

23


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Algorithm

variable expression

Syntax

variable = expression;

Rules

Expressions type must be the same as variables type

Valid Example: Invalid Example:

int x; int y;

x = 12; y = 5.75;


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Example:

int quantity;

float price_per_kg, price;

quantity = 5;

price_per_kg = 4.50;price = quantity * price_per_kg;

How does this

program work?


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Example:

int quantity;

float price_per_kg, price;

quantity = 2;

price_per_kg = 4.50;price = quantity * price_per_kg;


quantity ?

price_per_kg ?

price ?

4.50

9.00

2


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Example:

int number1, number2;

number1 = 25;

number2 = 23;

number1 = number2;

How does this

program

segment work?


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Constant

A value that will not change

Consists of:

Float(e.g. 2.3 2.73F 1.2e-5)

Integer (e.g. 3 67 -2)

Character(e.g. z 3 $ \n) String (e.g. UKM 1 5a)


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ExerciseTo practice what youve

learned, try exercises on

page 83 (Latih Diri)

from Pengaturcaraan C


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End of Lecture 4Whats next?INPUT ANDOUTPUTon the way

If you want to excel:revise chapter 4

read chapter 5 & 6 for next weekOtherwise, you may watch tv, sleep etc. as apreparation for next week classes.

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Slide 04 - Variables and Constants