Chapter Outline 1Boolean values 2Relational operators 3Simple Boolean expressions 4Logical operators 5Compound Boolean Expressions Precedence amp associativity 6Conditions ID: 776403
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Slide1
chapter 3
SELECTION CONTROL STRUCTURE
Slide2Chapter Outline
1.Boolean
values
2.Relational
operators
3.Simple
Boolean expressions
4.Logical
operators
5.Compound
Boolean Expressions
-Precedence
& associativity
6.Conditions
7.Types
of selection control structure
-One
way selection
-Two
way selection
-Multiple
selection
-
Multiway
selection (nested)
Slide3At the end of this class, student should be able to:Interpret the concept of relational and logical operatorsDifferentiate between three types of selectionProduce programs using selection controlIntroduce the nested if problem, explain the output based on the various input from the user.Solve a problem using multiway selection
Chapter Outcome
Slide4Allow flow of program to be altered, depending on one or more Boolean condition.The real intelligence of a computer comes from its ability to make decisions.No matter how complex a digital computer system seems to be, it’s only making simple Boolean decisions: on or off, 1 or 0 TRUE or FALSE.
Boolean Expression
Slide5Decision in a computer program is made by testing one condition against another.Example: if x<yHere, the condition of x is tested against the condition of y. If x is in fact less than y, the test result is true.However, if the value of x is greater than or equal to the value of y, the test is false.
Boolean Expression
Slide6To test condition within a program, you will use relational or logical operators to produce Boolean decision (TRUE or FALSE).When decisions are made in a computer program, they are simply the result of a computation in which the final result is either TRUE or FALSE. The value zero (0) is considered to be FALSE by C++. Any positive or negative value is considered to be TRUE. C++ evaluates any non-zero value to be TRUE.
Boolean Expression
Slide7In order to evaluate a comparison between two expressions we can use the Relational operators. As specified by the ANSI-C++ standard, the result of a relational operation is a boolean value that can only be true or false, according to the result of the comparison. When complex decisions must be coded into an algorithm, it may be necessary to “chain together” a few relational expression that use relational operators. This is done with logical operators (also known as Boolean Operators).
Relational Operators
Slide8Allow two quantities to be compared.Normally when the expression have 2 operands or identifiers, either same as, not same, small than, bigger than etc.
C++ OperatorMeaning==Equal!=Not equal to<Less than<=Less than or equal to>Greater than>=Greater than or equal to
Relational Operators
Slide9Example:
Statement(8 == 8) (3 > 7) (5!= 7) (6 >= 4) (9 < 9)
Resultwould return true. would return false. would return true. would return true. would return false.
Simple Boolean Expressions
Slide10More examples, instead of using only numeric constants, we can use any valid expression, including variables.Suppose that: a=4, b=2 and c=5
StatementResults(a == 4)would return true.(b*c>= a)would return true since (2*5 >= 4)(a+3 > a*b)would return false since (4+3 > 4*2).((c=2) == b)would return true.
Simple Boolean Expressions
Slide11#include<iostream.h>void main(){ cout<<(3+3 == 6)<<endl; cout<<(‘A’>’B’)<<endl; cout<<(4*10%2-5>25/5+3)<<endl; }OUTPUT:100
Example:
Relational Operators
Slide12Symbol
Operator
Description&& AND Both condition must be TRUE || OR Either one of the condition must be TRUE ! NOT Reverse condition
In order to evaluate a comparison between two logical expressions we can use the Logical Operators. If you need to test more that one relational expression at a time, it is possible to combine the relational expressions using the logical operators.
Logical Operators
Slide13First
OperandaSecondOperandbResulta && bResulta || btruetruetruetruetruefalsefalsetruefalsetruefalsetruefalsefalsefalsefalse
Logical Operators
Slide14#include<iostream.h>void main(){ cout<<((-2<0)&&(5>=10))<<endl; cout<<(((2-4)==2)||(!(3==6)))<<endl; }OUTPUT:01
If you need to test more than one relational expression at a time, it is possible to combine the relational expressions using the logical operators.
Compound Boolean Expression
Slide15A program is usually not limited to a linear sequence of instructions. During its process it may take decisions or repeat code. To make a decision or control a loop, a program must have conditions to determine its action. A condition is an expression which consists of relational operator and/or combines with logical operator to produce results whether TRUE or FALSE.The program will proceed with an action (instructions given by the programmer) based on the conditions result (TRUE or FALSE)Decision control can be solved using two methods:
if statement – The simples and most common selection structure is the if statement.switch statement- Is the alternative way and if the condition does not involved with relation or logical operator (used for integer numbers and single char only)
Condition Instruction
Slide16Type of selection control structure for if statements :One way selectionTwo way selectionMultiple selectionMultiway selection (nested if)
Condition Instruction
Slide17The if statement tests for a particular condition (expressed as a boolean expression) and only executes the following statement(s) if the condition is trueCompare just a selection which is written in a statement of the form: Example 1:
if (boolean-expression) statement;
cin>>score;if (score>=50) cout<<”PASS”;
One Way Selection -
if
Statement
Slide18An example follows of a fragment of a program which tests if the denominator is not zero before attempting to calculate fraction.If the value of total is 0, the boolean expression above is false and the statement assigning the value of fraction is ignored.
if (total!=0) fraction=counter/total;statement;
One Way Selection -
if
Statement
Slide19If a sequence of statements is to be executed, this can be done by making a compound statement or block by enclosing the group of statements in braces.Example 2:
if (boolean-expression){ statements;}
if (total !=0){ fraction = counter/total; cout<<”Proportion is =”<<fraction<<endl;}
One Way Selection -
if
Statement
Slide20#include<iostream.h>void main(){ char answer; cout<<”Do you want to enroll in this course(y=Yes/n=No)?”; cin>>answer; if(answer == ‘y’) { cout<<”You are now in CSC 128 class.\n”; cout<<”Welcome to the IT world!\n”; } if(answer == ‘n’) cout<<”Never mind.You can enroll later.\n”;} }
Example 3:
One Way Selection -
if
Statement
Slide21Often it is desirable for a program to take one branch if the condition is true and another if it is false.Compare two selection which is written in a statement of the form:Example 1:
if (boolean-expression) statement-1;else statement-2;
cin>>score;if (score>=50) cout<<”PASS ”;else cout<<”FAIL”<<endl;
Two Ways Selection –
If..else
Statement
Slide22If a sequence of statements is to be executed, this is done by making a compound statement by using braces to enclose the sequence:
if (boolean-expression){ statements;}else{ statements;}
Two Ways Selection
if..else
Statement
Slide23Example 2:
cin>>score;if (score>=50){ cout<<”CONGRATULATION!”; cout<<”YOU PASSED ”;}else cout<<”FAIL”<<endl;
Two Ways Selection
if..else
Statement
Slide24Two way selection using OR operator coding
#include<iostream.h>int main(){ char answer; cout<<”Can you play badminton?” cin>>answer; if(answer == ‘Y’ || answer == ‘y’) cout<<”You can join the club.\n”; else cout<<”Try again later.\n”; return 0;} }
Example 3:
Slide25Compare more than two selections which is written in a statement of the form
if (boolean-expression-1) Statement-1;else if (boolean-expression-2) Statement-2;else Statement-N;
Multiple Selection
Slide26Example 1:
#include<iostream.h>int main(){ int score; cout<<”Enter your total mark for CSC 128:”; cin>>score; if(score>=80) { cout<<”\nCongratulation!\n”; cout<<”You pass and get an A.\n”; } else if(score>=60) cout<<”You pass and get a B.\n”; else if(score>=50) cout<<”You pass and get a C.\n”; else { cout<<”Sorry\n”; cout<<”You fail\n”; } return 0;} }
Multiple Selection
Slide27Flow Chart:
if test 1 statement
else if test 2 statement
if Test 1
expression
else if
Test 2 expression
else if
Test n expression
else if test n statement
else statement
Next Statement
true
true
true
false
false
Multiple Selection
Slide28Multiple Selection
#include<iostream.h>void main(){ int number; cout<<”Enter a number:”; cin>>number; if(number>0) cout<<”positive number”; else if(number == 0) cout<<”zero number”; else cout<<”negative number”;} }
Example 2:
Slide29Multiple Selection using AND operator coding
Example 3:
#include<iostream.h>
void main()
{
int val1, val2, val3, max;
cout<<”Enter three integers:”;
cin>>val1>>val2>>val3;
if(val1>=val2 && val1>=val3)
max= val1;
else if(val2>=val1 && val2>= val3)
max= val2;
else if(val3>= val1 && val3>= val2)
max= val3;
cout<<”The maximum number is ”<< max<<endl;
}
}
Slide30Until now you already learn how to write one-way, two-way and many decision using if, if/else and if/else if/else statements respectively.Occasionally a decision has to be made on the value of a variable which has more than two possibilities. This can be done by placing if statements within other if-else constructions. This is commonly known as nesting and a different style of indentation is used to make the multiple-selection functionality much clearer. Additional decision options can be achieved by using nested if statements.A nested if statement is simply an if statement within an if statement.
Nested (
Multiway
) Selection
Slide31Written in a statement of the form:
if (boolean-expression-1)
if (boolean-expression-1) Statement-1; else Statement-2;else Statement-3;
Nested (
Multiway
) Selection
Slide32Example: A user enter temperature in degrees of Celsius and then determine if the temperature constitute water, steam or ice. Print “water” if the temperature is greater than 0 and less than 100, print “steam” if the temperature is greater and equal 100 and print “ice” if the temperature is less and equal to 0.
Nested (
Multiway
) Selection
Slide33ifTemp>0
if
Temp>=100
Print ICE
PRINT
Water
PRINT Steam
true
false
true
false
Answer: Flow Chart
Nested (
Multiway
) Selection
Slide34/*program to evaluate temperature whether it is water, steam or ice*/#include<iostream.h>void main(){ double temp; cout<<”Enter temperature in degree Celcius:”; cin>>temp; if(temp>0) { if(temp>=100) cout<<”STEAM\n”; else } cout<<”WATER\n”; else cout<<”ICE\n”;} }
Answer: Coding
Nested (
Multiway
) Selection
Slide35Example 2: Nation’s Air force has asked you to write a program to label supersonic aircraft as military or civilian. Your program is to be given the plane’s observed speed in km/h and its estimated length in meters. For planes traveling in excess of 1100km/h, you will label those longer than 52 meters “civilian” and shorter aircraft as “military”. For planes traveling at slower speeds, you will issue an “aircraft type unknown” message.
Nested (
Multiway
) Selection
Slide36Nested (Multiway) Selection
Slide37This last category of selection enables the program to select one of many options or cases.Normally we use switch statement to replace if statement if the condition does not involved with relational or logical operator (used for integer numbers and single char only)
switch
Statement
Slide38The syntax for switch statement is as followed:
switch (selector variable){ case value for case 1: Statement 1; .......; break; //to stop case1 case value for case n: Statement n; .......; break; //to stop case n default: //works as else in switch statement statement; break; //to stop default statement}
switch
Statement
Slide39Example 1:
switch Statement
#include<iostream.h>
void main()
{
char code_size;
cout<<”Enter your size:”;
cin>> code_size;
switch (code_size)
{
case ‘s’:
cout<<”Small Size”;
break;
case ‘M’:
cout<<”Medium Size”;
break;
default:
cout<<”Invalid Code”;
break;
}
cout<<”Hope you have identify your size";
}
}
Slide40Example 2:For more than one options in every cases (example: capital and small letters), the following example can be done.
switch Statement
#include<iostream.h>
void main()
{
char code_size;
cout<<”Enter your size:”;
cin>> code_size;
switch (code_size)
{
case ‘s’:
case ‘S’:
cout<<”Small Size”;
break;
case ‘M’:
case ‘m’:
cout<<”Medium Size”;
break;
default:
cout<<”Invalid Code”;
break;
}
cout<<”Hope you have identify your size";
}
}
Slide41Example 3: Using numbers in switch statement
switch Statement
#include<iostream.h>
void main()
{
int num;
cout<<”Enter your faculty level (1/2/3):”;
cin>>num;
switch (num)
{
case 1:
cout<<”You faculty is FKM”;
break;
case 2:
cout<<”You faculty is FKA”;
break;
case 3:
cout<<”You faculty is FSKM”;
break;
default:
cout<<"Invalid level"<<endl;
}
cout<<”Hope you are satisfied with your results!”;
}
}
Slide42Uses of break statement in switch StatementThe break statement causes the program to proceed to the first statement after the switch structure. Note that the switch control structure is different to the others in that braces are not required around multiple statements.
switch
Statement
Slide43Error in switch StatementWhat will happen if you do NOT put the ‘break’ statement in every cases?
switch Statement
#include<iostream.h>
void main()
{
char grade;
cout<<”Enter your grade:”;
cin>>grade;
switch (grade)
{
case ‘A’:
cout<<”Excellent”;
case ‘B’:
cout<<”Average”;
case ‘C’:
cout<<”Poor”;
case ‘F’:
cout<<”Try Again”;
}
cout<<”\nHope you are satisfied with your results!”;
}
}
Slide44Error in switch StatementThe compiler will return NO errors.But if one of the cases is TRUE and executed, the rest of cases also will be executed.
Enter a letter of grade: BAveragePoorTry AgainHope you are satisfied with your results!
switch
Statement
Slide45Question 1: Writing a boolean expression
Exercises
Expression
Result
bool
Q1=true, Q2=true, Q3=false;
Q1 || Q2 || Q3
144
<= 12 * 12
int
a=6, b=3, c=5;
i
. a==6&&b<3
ii
. b>=4 || c
==
5
iii
. 5<=a && b>3 || >=5
11 > 5 || 6 < 15 && 7 >= 8
Slide46Question 2:Show the output for each program segment below
int
m=6;
if (m < 2 * 5)
cout
<<”Win.”;
cout
<<”Lose.”;
int
x=8;
if ( x!= 8)
{
cout
<<”2 0 2 0”<<
endl
;
cout
<<”2 0 1 3”<<
endl
;
}
cout
<<”The End”<<
endl
;
Slide47Question 2:Show the output for each program segment below
int
x = 8;
if ( x >= 8)
x= x+2;
if ( x >= 10)
x= x-2;
if ( x >= 12)
x= x+2;
else
x=x-2;
Slide48Question 2:Show the output for each program segment below
int number = 5;if(number>2 && number<= 5) cout<<"first"<<endl; if (number < 7 && 3 > number) cout<< "second"<<endl; if(number<1||number>=number) cout<< "third"<<endl;
Slide49Question 2:Show the output for each program segment below
Slide50Question 3 :Write an appropriate C++ statement if. .else statements for each of the following:
If number is greater than 0, display message” Positif Number”, otherwise display message “Negatif Number”.
If gender code ‘F’ or ‘f’, display status “Female” and if gender code ‘M’ or ‘m’, display status “Male” . Otherwise, display “Invalid Code
”.
Slide51Question 3 :Write an appropriate C++ statement if. .else statements for each of the following:
If a number is even display the message “Number is Even” otherwise display the message “Number is Odd”.
Calculate amount of taxIncome based on the condition: If income up to RM15,000, tax= 0, if income between RM15,001 and RM25,000, tax = 5% and if income over RM25,000, tax = 10%
Slide52Question 4 Write a C++ program using the information in the table below to identify the IQ level. User has to enter IQ Scores.
Slide53Question 4 The National Earthquake Center has asked you to write a program implementing the following decision table to characterize an earthquake based on its Richter scale number.
The program accepts the Richter scale value and determines the earthquake characterization from the above table.
Slide54ANSWER
Slide55Question 1: Writing a boolean expression
Exercises : Answer
ExpressionResultbool Q1=true, Q2=true, Q3=false; Q1 || Q2 || Q3 1144 <= 12 * 12 1int a=6, b=3, c=5; i. a==6&&b<3 ii. b>=4 || c==5 iii. 5<=a && b>3 || c >=511 > 5 || 6 < 15 && 7 >= 8
0
1
1
1
Slide56Question 2:Show the output for each program segment below
int
m=6;
if (m < 2 * 5)
cout
<<”Win.”;
cout
<<”Lose.”;
Win.
Lose
int
x=8;
if ( x!= 8)
{
cout
<<”2 0 2 0”<<
endl
;
cout
<<”2 0 1 3”<<
endl
;
}
cout
<<”The End”<<
endl
;
The
End
Slide57Question 2:Show the output for each program segment below
int
x = 8;
if ( x >= 8)
x= x+2;
if ( x >= 10)
x= x-2;
if ( x >= 12)
x= x+2;
else
x=x-2;
6
Slide58Question 2:Show the output for each program segment below
&&&&----int number = 5;if(number>2 && number<= 5) cout<<"first"<<endl; if (number < 7 && 3 > number) cout<< "second"<<endl; if(number<1||number>=number) cout<< "third"<<endl; first third
Slide59Question 2:Show the output for each program segment below
TWOTHREEFOUR
Slide60Question 3 :Write an appropriate C++ statement if. .else statements for each of the following:
If number is greater than 0, display message” Positif Number”, otherwise display message “Negatif Number”.
if (number
> 0 )
cout<<“Positif Number”;
else
cout<<“Negatif Number”;
If gender code ‘F’ or ‘f’, display status “Female” and if gender code ‘M’ or ‘m’, display status “Male” . Otherwise, display “Invalid Code
”.
if (gender == ‘F’ || gender == ‘f’)
cout<<“Female”;
else if (gender ==‘M’ || gender ==‘m’)
cout
<<“Male’;
else
cout
<<“Invalid Code “;
Slide61Question 3 :Write an appropriate C++ statement if. .else statements for each of the following:
If a number is even display the message “Number is Even” otherwise display the message “Number is Odd”.
if (number % 2 == 0)
cout<<“Number is Even”;
else
cout<<“Number
is Odd”;
Calculate amount of taxIncome based on the condition: If income up to RM15,000, tax= 0, if income between RM15,001 and RM25,000, tax = 5% and if income over RM25,000, tax = 10%
if (income <= 15000)
tax = 0;
else if (income > 15001 && income
<=25000)
tax = 0.05;
else
tax = 0.10;
taxIncome = tax * income;
Slide62Question 4 Write a C++ program using the information in the table below to identify the IQ level. User has to enter IQ Scores.
Slide63#include <iostream.h>
void main()
{
int score;
cout<<"Enter the IQ Level : ";
cin>>score;
if (score< 20)
cout<<"Slow\n";
else if (score <=140)
cout<<"Normal \n";
else if (score <=210)
cout<<"Intelligent\n";
else
cout<<"Genius \n";
}
Slide64Question 4 The National Earthquake Center has asked you to write a program implementing the following decision table to characterize an earthquake based on its Richter scale number.
The program accepts the Richter scale value and determines the earthquake characterization from the above table.
Slide65#include <iostream.h>void main(){ double scale; cout<<"Enter Richter Scale Number : "; cin>>scale; if (scale < 5.0) cout<<"Little or no damage\n"; else if (scale <5.5) cout<<"Some damage \n"; else if (scale <6.5) cout<<"Serious damage: wall may crack or fall \n"; else if (scale<7.5) cout<<"Disaster: houses and building may collapse\n"; else cout<<"Catastrophe: most buildings destroyed \n";}
Answer:
Slide66#include <iostream.h>#include<string.h>void main(){ double scale; char status [50]; cout<<"Enter Richter Scale Number : "; cin>>scale; if (scale < 5.0) strcpy (status,"Little or no damage"); else if (scale <5.5) strcpy (status,"Some damage"); else if (scale <6.5) strcpy (status,"Serious damage: wall may crack or fall"); else if (scale<7.5) strcpy (status,"Disaster: houses and building may collapse"); else strcpy (status,"Catastrophe: most buildings destroyed"); cout<<status<<endl;}
Answer: using strcpy
Slide67Question 5Tracethe output for the progam given:
int p=10, q=5,r=10;
if (p>q && p<=r)
p = p + 1;
else
r = r + 1;
cout<<p<<" "<<r<<endl;
11 10
int number = 5;
if(number>2 && number<= 5)
cout<<"first"<<endl;
if (number < 7 && 3 > number)
cout<< "second"<<endl;
if(number<1||number>=number)
cout<< "third"<<endl;
first
third
Slide68TWOTHREEFOUR
Slide69THANK YOU