Unit 3 Understand selection control structures

At the end of this presentation, students will be able to:• Understand selection control structures• Describe the structure and working of simple if

statements• Describe the structure and working of nested if

statements• Describe the structure and working of switch

statements

Statements executed one by one. Simplest Example :

int x = 5; [S1]int power = x*x; [S2]cout << “\n” << power; [S3]

S3S2S1Entry

Exit

C++ supports two types of program control:• selection control structures• looping control structures

Purpose:• to evaluate expressions/condition • to direct the execution of the program (depending

on the result of the evaluation). The most commonly used selection

statements are: • if statement• if-else statement• nested-if statement• switch statement

Used to execute a set of statements when the given condition is satisfied.

Syntaxif (<condition>)

{

<Conditional statements>;

} Conditional statements within the block

are executed when the condition in the if statement is satisfied.

truecondition

Conditional statement

Next statement

false

Example:if (age > 21)

cout << “\n Anda layak mengundi”;

trueage > 21

Anda layak mengundi

Next statement

false

Program InputValue.cpp illustrates the execution of a simple if statement. The program checks whether the given number is greater than 100.

number<100false

true

start

Declare: number variable

Read number

Print result “Number is less

than 100”

end

#include <iostream> using namespace std;

int main() { int num; cout << "Enter integer number: "; cin >> num; if(num<100)

cout<<"Number is less than 100"<<endl;

return 0; }

Executes the set of statements in if block, when the given condition is satisfied.

Executes the statements in the else block, when the condition is not satisfied.

Syntaxif (<condition>){

<Conditional statements1>;}else{

<Conditional statements2>;}

true

condition

Next statement

false

Conditional statement in else body

Conditional statement in if body

Example:if (E4162 == ‘L’)

cout << “\n Anda lulus”;else

cout << “\n Anda gagal”;

Next statement

falsetrue

Anda gagalAnda lulus

E4162 == ‘L’

Program Checks.cpp illustrates the use of the if-else statement. This program accepts a number, checks whether it is less than 0 and displays an appropriate message.

number<0falsetrue

start

Declare: number variable

Read number

end

Print “Positive”

Print “Negative”

#include <iostream> using namespace std;

int main() { int num; cout << "Enter integer number: "; cin >> num; if(num<0)

cout<<"Negative"<<endl; else

cout<<"Positive"<<endl;

return 0; }

1. Accept a number from the keyboard and check whether it is dividable by 5 (if else).Hint: Use the modulus operator, %, to check the divisibility.

#include <iostream>using namespace std;

int main(){

int no;

cout<<"Enter integer number: ";cin>>no;

if(no%5==0)cout<<"dividable by 5"<<endl;

elsecout<<"undividable by 5"<<endl;

return 0;}

2. Accept two integer numbers from the keyboard and find the highest among them.

#include<iostream>using namespace std;

int main(){

int no1,no2;cout<<"Enter two integer number: ";cin>>no1>>no2;

if(no1>no2)cout<<"Number 1 is highest than number

2"<<endl;else

cout<<"Number 2 is highest than number 1"<<endl;

return 0;}

The if statements written within the body of another if statement to test multiple conditions is called nested if.

Syntax if (<Condition 1>){ if (<Condition 2>) {

<Conditional statements1>; } else

{ <Conditional statements2>; }

}else{ <Conditional statements3>;}

Inner if condition Outer if

condition

Conditional statements1

falsetrue

Condition 1

Condition 2

true

Conditional statements2

Next statement

false

Conditional statements3

The program Highest.cpp illustrates the use of nested if statements. The program accepts three integers from the user and finds the highest among the three.

#include <iostream>using namespace std;

int main(){

int x,y,z;

cout<<"Enter x: ";cin>>x;cout<<"Enter y: ";cin>>y;cout<<"Enter z: ";cin>>z;

if(x>y){

if(x>z) cout<<x<<" is the highest"; else

cout<<z<<" is the highest"; }

else {

if (y>z)cout<<y<<" is the highest";elsecout<<z<<" is the highest";

}

return 0;}

#include <iostream>using namespace std;

int main(){

int x,y,z;

cout<<"Enter x: ";cin>>x;cout<<"Enter y: ";cin>>y;cout<<"Enter z: ";cin>>z;

if(x>y&&x>z) cout<<x<<" is the highest";

else if (y>x&&y>z) cout<<y<<" is the highest";

else

cout<<z<<" is the highest";

return 0;}

#include <iostream>using namespace std;

int main(){

int a,b,c;

cout<<"Enter a: ";cin>>a;cout<<"Enter b: ";cin>>b;cout<<"Enter c: ";cin>>c;

if(a>c&&b>c){if(a>b)

cout<<a<<" is the highest";else

cout<<b<<" is the highest";}

else{if(c>a&&c>b)

cout<<c<<" is the highest";

else cout<<b<<" is the highest";

}return 0;

}

#include<iostream>using namespace std;void main(){

int x=2;if(x<=3)

if(x!=0)cout << "Hello";

else cout<< "hello";

if(x>3)if(x!=0)

cout << "Hi";else

cout << "hi";}

Note that the first line does not end with a semicolon.

The curly brackets are necessary only if there are several statements.

Switch statement is C++'s multi-way branch

Allows to specify a number of different cases, rather than simply true or false

Switch statement requires an expression after the word switch and then it jumps to the statement whose case matches the expression

A break statement passes the control outside switch structure.

Syntaxswitch (expression) { case expression_1 :

statement sequence; break;

case expression_2 : statement sequence;

break; ………….. case expression_n :

statement sequence; break;

default : statement sequence;

}

expression_1

expression_2

statement sequence

statement sequence

break

break

default

break

Example:

int main(){char pilih;cout << “\n Menu Utama\n”;cout << “ M = Masukkan duit \n”;cout << “ K = Keluarkan duit\n”;cout << “ E = Exit\n”;cout << “ Pilihan anda: “;cin >> pilih;switch (pilih)

{case ‘M’ : cout << “Sila tambah duit anda”;break;case ‘K’ : cout << “Hanya boleh keluar

duit”;break;case ‘E’ : cout << “Keluar dari Menu

Utama”;break;default : cout << “Pilihan yang salah”;}

}

Program SwitchDemo.cpp illustrates switch case execution. In the program, the switch takes an integer value as input and displays the month based on the integer entered.

#include <iostream>using namespace std;

int main(){

int month;

cout<<"Enter number: ";cin>>month;

switch (month) { case 1: cout<<"January";

break; case 2: cout<<"February"; break; case 3: cout<<"March"; break; case 4: cout<<"April"; break;

default: cout<<"wrong choice";}return 0;

}

1. Write a program to accept number of a day for the week and print the day

1 – Sunday 5 – Thursday2 – Monday 6 – Friday3 – Tuesday 7 – Saturday4 - Wednesday

#include <iostream>using namespace std;

int main(){

int day;

cout<<"Enter number: ";cin>>day;

switch (day) { case 1: cout<<"Sunday";

break; case 2: cout<<"Monday"; break; case 3: cout<<"Tuesday"; break; case 4:

cout<<"Wednesday"; break;

case 5: cout<<"Thursday";

break; case 6:

cout<<"Friday"; break; case 7:

cout<<"Saturday"; break;

default: cout<<"wrong choice";

}return 0;

}

Write a program that able to check either a character is a vowel or not by using switch statements and if else statement

#include <iostream>using namespace std;

int main(){

char ch;

cout<<"Enter character: ";cin>>ch;

switch (ch) { case 'a': case 'A': cout<<"Vowel";

break; case 'e': case 'E': cout<<"Vowel"; break; case 'i': case 'I': cout<<"Vowel"; break;

case 'o': case 'O': cout<<"Vowel";

break;case 'u': case 'U': cout<<"Vowel";

break;default: cout<<"Not vowel";

} return 0;}

#include<iostream>using namespace std;

void main(){

char ch;

cout<<"Enter character: ";cin>>ch;

if(ch=='a'||ch=='A'||ch=='e'||ch=='E'||ch=='i'||ch=='I'||ch=='o'||ch=='O'||ch=='u'||ch=='U')

cout<< ch << " is a vowel\n";else

cout<< ch << " is not a vowel\n";

}

In this presentation, you learnt the following: Program controls are used to change

the sequential flow of a program. The two types of program controls are

selection control structures and looping control structures

In C++, the selection control structures include if and switch statements.