Lec11_Expressions &Control Structures

7/31/2019 Lec11_Expressions &Control Structures

1/40

One major use of AND operation is for

placing 0s in one part of a bit pattern while

not disturbing the other part.

For example 00001111 without knowing the second operand we can say

that the first four most significant bits will be 0s

Moreover the four least significant bits will be a

copy of the second operand.

2-1


2/40

00001111

AND 1010101000001010

2-2


3/40

This use of the AND operation is called

masking.

Here one operand, called the mask,

determines which part of the other operandwill affect the result.

In case of AND operation, masking produces a

result that is a partial replica of the one

operand, with 0s occupying thenonduplicated positions.

2-3


4/40

Such an operation is useful when

manipulating a bit map,

A string of bits in which each bit represents the

presence or absence of a particular object

We have encountered bit maps in context of

representing images, where each bit is

associated with a pixel.

2-4


5/40

Where AND operation can be used to

duplicate a part of bit string while placing 0s

in the nonduplicated part

The OR operation can be used to duplicate apart of a string while putting 1s in the

nonduplicated part

For example 11110000

Produces 1s in four most significant bits While remaining bits are copied in the four least

significant bits.

2-5


6/40

11110000

OR 1010101011111010

2-6


7/40

A major use of XOR operation is in the

forming of complement of a bit string

XORing any byte with a mask of all 1s

produces the complement of the byte.

2-7


8/40

11111111

XOR1010101001010101

2-8


9/40

Suppose you want to isolate the middle 4 bits

of a byte by placing 0s in the other 4bits

without disturbing the middle 4bits. What

mask must you use together with thatoperation?

1-9

00000000

00111100


10/401-10

00111100Apply masking with?

AND

Because in AND operations we put

0s where we dont want to change

the bits.


11/40

Expressions / mixed expressions and

casting (Implicit and Explicit casting),

Post fix and Pre fix Operators

Control structures. If, if-else, nested if,


12/40

How expressions involving mixed types of dataare evaluated.

int value1=10;

long value2 =25L;

float value3= 30.0f;

double result=value1+value2+value3;

The value of result is calculated as the sumof three different types of variables.

For each add operation, one of the operandswill be converted to the type of the otherbefore addition can be carried out.

12


13/40

The statement in the previous slide is actuallyexecuted with the steps: value1+ value2 is calculated by convertingvalue1 to type long before the addition. Theresult is also of type long, so the calculation is10L+25L=35L

The next operation is 35L+value3. Theprevious result, 35L is converted to type float

so 35.0f+30.0f=65.0f

Finally 65.0f is converted to double an stored inresult.

13


14/40

The rules for dealing with mixed

expressions apply only when the types of

the operands for a binary operations are

different. Rules in the sequence in whichthey apply are as following:

If either operand is of type long double, the

other us converted to long double.

If either operand is of type double, the otherus converted to double.

If either operand is of type float, the other

us converted to float.

14


15/40

Any operand of type char, signed char,unsigned char, short or unsigned short

is converted to type int, as long as type int can

represent all values of the original operand type.Otherwise, the operand is converted to unsigned

int.

An enumeration type is converted to the first int,

unsigned int, long or unsigned long that

accomodates the range ofenum.

If either operand is of type unsigned long, theother us converted to unsigned long.

15


16/40

If one operand is type long and the other isunsigned int, then provided type long can

represent all values it is converted to type long

otherwise unsigned long.

If either operand is of type long, the other usconverted to long.

16


17/40

The basic idea is very simple. With twooperands of different types the type with thelesser range of values is converted to theother. The formal rules roughly boil down to:

if the operation involves two different floating pointtypes, the one with the lesser precision will bepromoted to the other.

If the operations involves an integer and a floatingpoint value, the integer will be promoted to the

floating point type. If the operation involves mixed integer types, the

type with the more limited range will be promoted tothe other.

If the operation involves enumerations they will be

converted to a suitable integer type.17


18/40


19/40

short a=2000;

int b;

b = (int) a; // c-like cast notation

b = int (a); // functional notation

19


20/40

Expression LHS Value

int1 = 7; int2 = 2;float1 = int1 / int2 + 5; 8.0

int1 = 3.8; 3

float2 = float(int1)/int2 +5 8.5

float1 = 5; 5.0

Implicit castingType casting


21/40

Both the increment operator (++) and the

decrement operator(--) come in two

varieties:

Prefix and postfix. The prefix variety is written before the variable

name (++myAge);

Variable is changed, then the expression it is in is evaluated.

The postfix variety is written after(myAge++)

Expression the variable is in executes, then the variable is

changed.

21


22/40

Increment operator (++)

Increment variable by one

c++

Same as c += 1

Decrement operator (--) similar

Decrement variable by one

c--

22


23/40

Ifc = 5, then

cout


24/40

24


25/40

25


26/40

26

3 control structures

Sequence structure

Programs executed sequentially by default

Selection structures

if, if/else, switch

Repetition structureswhile, do/while, for


27/40

27

C++ keywords

Cannot be used as identifiers or variable namesC++ Keywords

Keywords common to theC and C++ programming

languagesauto break case char const

continue default do double else

enum extern float for goto

if int long register return

short signed sizeof static struct

switch typedef union unsigned void

volatile while

C++ only keywordsasm bool catch class const_cast

delete dynamic_cast explicit false friend

inline mutable namespace new operator

private protected public reinterpret_cast

static_cast template this throw true

try typeid typename using virtual

wchar_t


28/40

28

Flowchart

Graphical representation of an algorithm

Special-purpose symbols connected by arrows

(flowlines)

Rectangle symbol (action symbol)

Any type of action

Oval symbol

Beginning or end of a program, or a section of code

(circles)

Single-entry/single-exit control structures

Connect exit point of one to entry point of the

next


29/40

29

Selection structure

Choose among alternative courses of action

Pseudocode example:

If students grade is greater than or equal to 60

Print Passed

If the condition is true

Print statement executed, program continues to next

statement

If the condition is false Print statement ignored, program continues

Indenting makes programs easier to read

C++ ignores whitespace characters (tabs, spaces, etc.)


30/40

30

Translation into C++If students grade is greater than or equal to 60

Print Passed

if ( grade >= 60 )cout


31/40

31

Flowchart of pseudocode statement


32/40

32

if Performs action if condition true

if/else Different actions if conditions true or false

Pseudocodeif students grade is greater than or equal to 60print Passed

else

print Failed

C++ codeif ( grade >= 60 )cout


33/40

Ternary conditional operator (?:)

Three arguments (condition, value iftrue,

value iffalse)

Code could be written:cout= 60 ? Passed : Failed );

truefalse

print

Failed

print

Passed

grade >= 60

Condition Value if true Value if false


34/40

34

Nested if/else structures

One inside another, test for multiple cases

Once condition met, other statements skippedif students grade is greater than or equal to 90

Print Aelse

if students grade is greater than or equal to 80Print B

else

if students grade is greater than or equal to 70Print C

else

if students grade is greater than or equal to 60Print D

else

Print F


35/40

35

Example

if ( grade >= 90 ) // 90 and above

cout = 80 ) // 80-89

cout = 70 ) // 70-79

cout = 60 ) // 60-69

cout


36/40

36

Compound statement Set of statements within a pair of bracesif ( grade >= 60 )

cout


37/40

What is wrong with the following if

statement

1-37

if numNeighbors >= 3

++numNeighbors;

cout


38/40

Describe the output

1-38

int number = 4;

double alpha = -1.0;if (number > 0)

if (alpha > 0)

cout


39/40

1-39

int number = 4;

double alpha = -1.0;

if(number > 0)

{ if(alpha > 0)cout


40/40

Using if-else statement write program that

calculates the following:

Addition

Subtraction

Multiplication

Division

When a user writes addition is adds and so on

Lec11_Expressions &Control Structures

Documents

Transcript of Lec11_Expressions &Control Structures