1. Unit 3
Understand selection control structures

2.  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

3.  Statements executed one by one.
 Simplest
 Example :
int x = 5; [S1]
int power = x*x; [S2]
cout << “n” << power; [S3]
Entry S1 S2 S3 Exit

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

5.  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

6.  Used to execute a set of statements when
the given condition is satisfied.
Syntax
if (<condition>)
{
<Conditional statements>;
}
 Conditional statements within the block are
executed when the condition in the if
statement is satisfied.

7. false
condition
Conditional statement
true
Next statement

8.  Example:
if (age > 21)
cout << “n Anda layak mengundi”;

9. false
age > 21
Anda layak mengundi
true
Next statement

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

11. start
Declare: number variable
Read number
false
number<100
true
Print result “Number is
less than 100”
end

12. #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;
}

14.  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.
Syntax
if (<condition>)
{
<Conditional statements1>;
}
else
{
<Conditional statements2>;
}

15. true false
condition
Conditional statement in else
Conditional statement in if body
body
Next statement

16.  Example:
if (E4162 == ‘L’)
cout << “n Anda lulus”;
else
cout << “n Anda gagal”;

17. true false
E4162 == ‘L’
Anda lulus Anda gagal
Next statement

18.  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.

19. start
Declare: number variable
Read number
true false
number<0
Print Print
“Negative” “Positive”
end

20. #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;
}

21. 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.

22. #include <iostream>
using namespace std;
int main()
{
int no;
cout<<"Enter integer number: ";
cin>>no;
if(no%5==0)
cout<<"dividable by 5"<<endl;
else
cout<<"undividable by 5"<<endl;
return 0;
}

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

24. #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;
}

25.  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>; Inner if
}
} condition Outer if
else
{ condition
<Conditional statements3>;
}

26. false
Condition 1
true
false
Condition 2
true
Conditional Conditional
Conditional statements1
statements2 statements3
Next statement

27.  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.

28. #include <iostream>
using namespace std; if(x>y)
{
int main() if(x>z)
{ cout<<x<<" is the highest";
int x,y,z; else
cout<<z<<" is the highest";
cout<<"Enter x: "; }
cin>>x; else
cout<<"Enter y: "; {
cin>>y; if (y>z)
cout<<"Enter z: "; cout<<y<<" is the highest";
cin>>z; else
cout<<z<<" is the highest";
}
return 0;
}

29. #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;
}

30. #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;
}

31. #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";
}

32.  Note that the first line does not end with a
semicolon.
 The curly brackets are necessary only if
there are several statements.

33.  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.

34. Syntax
switch (expression)
{
case expression_1 :
statement sequence;
break;
case expression_2 :
statement sequence;
break;
…………..
case expression_n :
statement sequence;
break;
default :
statement sequence;
}

35. statement
expression_1 break
sequence
statement
expression_2 break
sequence
default
break

36.  Example:
int main()
{
char pilih;
cout << “n Menu Utaman”;
cout << “ M = Masukkan duit n”;
cout << “ K = Keluarkan duitn”;
cout << “ E = Exitn”;
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”;
}
}

37.  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.

38. #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;
}

39. 1. Write a program to accept number of a
day for the week and print the day
1 – Sunday 5 – Thursday
2 – Monday 6 – Friday
3 – Tuesday 7 – Saturday
4 - Wednesday

40. #include <iostream> case 5: cout<<"Thursday";
using namespace std;
break;
int main() case 6: cout<<"Friday";
{
int day; break;
case 7: cout<<"Saturday";
cout<<"Enter number: "; break;
cin>>day;
default: cout<<"wrong
switch (day) choice";
{ }
case 1: cout<<"Sunday";
break; return 0;
case 2: cout<<"Monday"; }
break;
case 3: cout<<"Tuesday";
break;
case 4: cout<<"Wednesday";
break;

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

42. #include <iostream>
using namespace std;
int main()
{
case 'o':
char ch;
case 'O': cout<<"Vowel";
break;
cout<<"Enter character: ";
cin>>ch; case 'u':
case 'U': cout<<"Vowel";
switch (ch) break;
{ default: cout<<"Not vowel";
case 'a': }
case 'A': cout<<"Vowel"; return 0;
break; }
case 'e':
case 'E': cout<<"Vowel";
break;
case 'i':
case 'I': cout<<"Vowel";
break;

43. #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 voweln";
else
cout<< ch << " is not a voweln";
}

44. 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.