12 - Control Structure

8/2/2019 12 - Control Structure

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Operators and ControlStructures


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On the menu today

I- Quick reviewII- Relational & logical operators

III- Control Structure


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I- Review


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A- Variables declaration

What is required?

Three rules to declare a variable

Good habits for a variable name


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How can we get a value into this variable

B- Variables assignment

1- variable = expression;it means: variable expression

(value of the expression assigned to

the variable)


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C- Types of expression

Provide the different types of expression:

- numeric constant

- another variable- arithmetic expression

operand operator operand


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II- Relational & logical operators


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A- Relational operators

Goal: Compare or Write conditions

Relational expression: operand operator operand

Different operators

< less than> greater than

= greater than or equal to== equal to

!= not equal to


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A- Relational operators: example

Relational expressions

- (4 < 3) less than

- (firstInitial != 'A') not equal

- (hoursWorked > 40) greater than

- (pollutionIndex >= cutoff) greater than or equal

- (age


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B- Logical operators

Goal: Create more complex conditions

&& and

|| or

! not


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B- Logical operators: Example

Logic expressions

(age > 40) && (height > 1.75)

(age > 40) || (height > 1.75) || (weight > 80)

! ((age > 40) && (height > 1.75))


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left to right

* / %

+ -

< >=

== !=

&&||

C- Operators precedence


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C- Expression value and interpretation

relational and logical expression take

value 1 0

interpreted in true false


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C- Expression value andinterpretation: Example

int i = 5, j = 7, k = 12;

Expression equivalent value interpretationexpression

i+1==k+1 (i+1)==(k+1) 0 false

3*1-jk 1 true

k+3


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Lecture 4

II- Program Control

Structure


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A- Syntax form

//Syntax form of a C++ program# include

definitions, declarations and

functions

void main()

{declarations and statements

}


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B- Control Structure: what for?

We can think of a program as a set ofstatements that manipulate variables.

How to control the order in which thosestatements execute?

Goal: Control the order of thestatements


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B- Control Structure: 3 Types

Sequences:

By default, they execute sequentially

Selection : Condition - DecisionWe can force them to execute selectivelyconditionally

Iteration: LoopWe can force them to execute iteratively


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C- Sequences# include

void main()

{

float a, b, c;

a = 12.0;b = 15.0;

c = (a + b) / (a - b);

cout


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Does the order of statements matter ?

C- Sequences

Yes, the statements are executed insequence.


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C- Selection

- Sometimes we only want to execute astatement under certain conditions.

- That is, we want to selectivelyexecute astatement or a series of statements.

C S


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-We informally think of this as an "if...then"situation:

if (condition)statements to execute if condition is true

else

statements to execute if condition is false

C- Selection

C S l i


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C- Selection- Flow diagrams are good for capturing this idea:

- The condition states a question whose answer isYes/True or No/False.

condition

Statement

to be executed

when condition

is false

Statement

to be executed

when condition

is true

N Y

C S l i l


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if hours worked is greater than 40

compute regular hours as 40

compute overtime hours as hours worked - 40

compute earnings as regular hours * wage rateplus overtime hours * 1.5 * wage rate

otherwise

compute earnings as hours worked * wage rate

C- Selection: example

C S l i l


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hrsworked > 40

?

earnings hrsworked* wageRate

reghours 40

othours hrsworked -40

earning reghours *wageRate

+ othours*1.5* wageRate

N Y

C S l i l


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Scenario: Three pollution levels called reading1,reading2, and reading3. An air pollution index isdefined as the average of these readings. Any air

pollution index less than the cutoff means air quality issafe; otherwise it is hazardous.

Assume values already in all four variables:reading1,reading2, reading3, and cutoff.

C S l ti l


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Example:

float Index;

Index = (reading1+ reading2+ reading3)/3;if (Index < cutoff)

cout


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C- Selection - ifStatement : twotypes

condition

Statements

N Y

if (condition){

statements;

}

C S l ti if


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condition

Statements

N Y if (condition){

statements;}

else

{statements;

}

Statements

C- Selection - ifStatement : two types

D It ti


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D- Iteration: why we need loops

Let's write a program to print out

a chart of the first 10 positive integers

and their squares.

D It ti


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Lecture 4


#include void main(){

cout


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Observations?

D It ti h d l


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D- Iteration: why we need loopsModified version:

#include void main(){

int x = 1;cout


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Observations?

We are repeating exactlythe same two statementsten times.

Alternative?x 0;loop while x < 10

add 1 to xreport x and x2

end loop


D Iteration h d l


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Observations?

a) we have found the patternandonly written that

b) we have let the computer do thework


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Questions?

12 - Control Structure

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