Slide 06 - Operators and Expressions

8/10/2019 Slide 06 - Operators and Expressions

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Computer Science Department FTSM

Operators andExpressions

Knowledge:

Know the types of basic arithmetic operators and their order of precedence

Skill:

Develop skills in computer arithmetic



TK1913-C Programming 2

We use arithmetic expressions to solve

most programming problems

Arithmetic expressions comprise of

operators and operands

There are rules for writing andevaluating arithmetic expressions

Introduction




Operator and Operand

Example:

W + Z

Operand

Operator

Operand

What are operator and operand?




Example:

Operator and OperandWhich is which?

A / B

Operator ??

Operand??




Basic Arithmetic Operators Multiplication, addition and subtraction are

the simplest to use

Division is easy, but some precautions need to

be taken

Modulus is the one that normally confuses

novices

So, let’s study in detail the Division and Modulus




DivisionExample:

W / Z

Floating Division

W or Z or both are

floats

Integer Division

W and Z are integers




Example:Integer Division

8 / 2 = 4

an integer

an integer

the result isalso an integer




Example:Integer Division

12 / 5 = 2

an integer

an integer

the result isalso an integer




Example:Floating Division

12.0 / 5 = 2

a float

an integer

the result is a

float




What will be the answer

if an integer is dividedby 0? How about if one

of the operands is a

negative integer?

Something to ponder …




Modulus

It returns the remainder that occurs

after performing the division of 2

operands

Rule: Operands must be integers




Example:

Modulus

12 % 5 = 2

an integer

an integer

the result is theremainder of 12/5

125

2

102

remainderresult




Example:

Modulus

7 % 3 = 1

an integer

an integer

73

2

61

remainderresult

the result is theremainder of 7/3




Example:

Modulus

12.0 % 3 = ??

a float

an integer

INVALID!




The earlier expressions

contain only oneoperator at a time. What

if the expression

contains more than one

operator?

Something to ponder …




An expression may contain 2 or more

arithmetic operators

Main issue:

ORDER OF PRECEDENCE

Arithmetic Expression




Examples:

5 + 6

5 + 6 * 2

2.5 + 6 – 2 * 2

12 / 6.0 – 2 * 2

= 11

= 22 or 17?

= ??

= ??

= 17





Arithmetic ExpressionOrder of Precedence:

High: * / %

Low: + -

All operators have a precedence level. High

precedence level operators are evaluated beforelower ones. Operators of the same precedence levelare evaluated from left to right




Example:

Try it!

12 + 6.0 – 2 * 2 = ??

What’s the answer??





All expressions in parentheses (brackets) must

be evaluated prior to values outside brackets

Nested parenthesized expressions must be

evaluated from the inside out, with the

innermost expression evaluated first

Example:

( 9 – ( 3 + 2 ) ) * 3 = ??





Example:

( 9 – ( 3 + 2 ) ) * 3 = ?? – 54 12( 9 – ( 3 + 2 ) ) * 3 = 12




Assignment Statement

There are 3 types of assignment:

Simple

Multiple

Shorthand



Buying price:

Buying price: 10 00

Buying price: 10 00

Buying price: 10 00

Buying price: 10 00

Buying price: 10.00




Simple AssignmentExample:

#include <stdio.h>

void main( ) {

float price, discount, total;

printf(“Buying price : “);

scanf(“%f”, &price);

printf(“\nDiscount rate : “);

scanf(“%f”, &discount);

total = price – (price * discount);printf(“\nFor buying price RM%.2f and discount rate %.2f\n”,

price, discount);

printf(“The total price is RM%.2f \n”, total);

}

Buying price: _

discount ??

price ??

total ??

Buying price: 10.00

_

10.00

Buying price: 10.00

Discount rate: _

Buying price: 10.00

Discount rate: 0.25

_

0.25

7.50

Buying price: 10.00

Discount rate: 0.25

For buying price RM10.00 and discount rate 0.25

_

Buying price: 10.00

Discount rate: 0.25

For buying price RM10.00 and discount rate 0.25

The total price is RM7.50

_




Syntax:

variable = variable = expression ;

Multiple Assignment

Don’t forget the semicolon !!




Shorthand Assignment

Syntax:

variableX = variableX op expression ;

variableX op = expression;




Whenever the expression on the right contains the

variable on the left (to which the value is assigned)

Example:

num = num + 5;

num 15

15 + 5

20

20





Expressions can also be stated using shorthand

assignment operators

Example:num += 5; similar to num = num + 5

shorthand assignment operator


Shorthand assignment operators have the lowest

order of precedence – the last one to be evaluated




Operation Examples of

expression

Description

+= num += 5; num = num + 5;

-= num -= 5; num = num – 5;

*= num *= 5; num = num * 5;

/= num /= 5; num = num / 5;

%= num %= 5; num = num % 5;





Example:

pay += hour * rate * 2

pay + (8 * 5.00 * 2)

pay 100.00

hour 8

rate 5.00

similar to pay = pay + (hour * rate * 2)

pay + (hour * rate * 2)

100.00 + 80.00

180.00

180.00





Assignment by Value

Every assignment expression has a value

Example:

Expression 1: a = 1;

Expression 2: x = y = 0;

Expression 3: p = 12;

p = 0;

Example:

int a, x, y, p;

Line 1: a=1;

Line 2: x = y = 0;

Line 3: p = 12;Line 4: p = p +3;

Line 5: q = p = p + x;




Relational OperatorsOperation Description Examples

of

Expression

Value

< Less than 6 < 9 1 (true)<= Less than or equal to 5 <= 5 1 (true)

> Greater than 2 > 6 0 (false)

>= Greater than or equal to 9 >= 5 1 (true)

== Equal to 7 == 5 0 (false)

!= Not equal to 6 != 5 1 (true)




Compound Statement

Arithmetic, relational and mantic operators can be

integrated/combined in one expression

Example:

! ( c > a )a 2

b 5

c 15

d 17! ( 1 )

! ( 15 > 2 )

0




Example:

(a >= 1) && (b == 5)

a 2

b 5

c 15

d 17

( 2 >= 1 ) && ( b == 5 )

Compound Statement

1 && ( b == 5 )

1 && ( 5 == 5 )

1 && 1

1




Example:

(c >= ( b * 3 ) ) || (a == 3)

a 2

b 5

c 15

d 17

( c >= ( 5 * 3 ) ) || ( a == 3)

Compound Statement

1 || ( a == 3 )

1 || ( 2 == 3 )

1 || 0

( 15 >= 15 ) || ( a == 3)

1




Example:

! ( ( a < b ) || ( c > d ) )

a 2

b 5

c 15

d 17

! ( ( 2 < 5 ) || ( c > d ) )

Compound Statement

! ( 1 || ( 15 > 17 ) )

! ( 1 || 0 )

! 1

! ( 1 || ( c > d ) )

0




Increment and DecrementThis operation contains only one operand, that is,the operand which value will be incremented/

decremented

Symbol Description Examples of

Expression

Description

++ Increment

operand by 1

i++ i = i + 1

-- Decrement

operand by 1

i-- i = i – 1




Key-in a number: _Key-in a number: 26

_

Increment and DecrementExample:

int num;

printf(“Key-in a number: “);

scanf(“%d”, &num); printf(“Value before being incremented: %d\n”, num);

num++;

printf(“Value after being incremented: %d”, num);

num ??

Key-in a number: 26

Value before being incremented: 26

_

2627

Key-in a number: 26

Value before being incremented: 26

Value after being incremented: 27 _




Prefix and PostfixIncrement and Decrement operators can be either in prefix or

postfix forms

Expression Description

i++ Value of i is incremented after being used in the

expression

++i Value of i is incremented before being used in the

expression

i-- Value of i is decremented after being used in theexpression

--i Value of i is decremented before being used in the

expression




Example:

j = i++ - 2

i 5

similar to

j = i – 2;

i = i + 1;

Prefix and Postfix

j ??3

6




Example:

j = ++i - 2

i 5

similar to

i = i + 1;

j = i – 2;

Prefix and Postfix

j ??4

6




Example:int x = 10;

float y;

y = (float) x;

Coersion

( float ) 10

10.000000

x 10

y ??10.000000

Coersion is used to compute a value that is equivalent

to its operand’s value (based on the stated data type)




Example:

int total, number;

float average;

…

average = total / number;

Coersion

15 / 2

7

total 15

number 2

average ??7.000000




Example:

int total, number;

float average;

…

average = (float) total / number;

Coersion

15.000000 / 2

7.500000

total 15

number 2

average ??7.500000



End of Lecture 6

Yes !! That’s all?What’s next???

CONTROL STRUCTURE:

SELECTION on the way …

Slide 06 - Operators and Expressions

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