CONTROL STRUCTURES
(SELECTION)
PROGRAM COMPONENTS
SEQUENCE
Groups Of Sequential Steps
SELECTION
Making Choices
IF-THEN (one way)
IF-THEN-ELSE (two way or multi way)
SWITCH (multi way)
ITERATION(Looping)
Repeating Steps
WHILE – DO (top tested)
DO – WHILE (bottom tested)
FOR (fixed iteration)
BOOLEAN DATA TYPE
Two Values – true (1) or false (0)
Example:
bool isOvertime = true;
cout << “Is overtime “ << isOvertime << endl;
isOvertime = false;
cout << “Is overtime “ << isOvertime << endl;
Internal program value
Cannot be read in via keyboard entry
Only displayed as 1 or 0
BOOLEAN DATA TYPE
Boolean names should reflect true value
For example:
bool done = false;
bool even = false;
bool error = true;
Can be initialized with integer:
Using 0 intializes to false
Anything Else initializes to true
It is best to use values true or false
RELATIONAL / EQUALITY
OPERATORS
Boolean expression is:
A condition in which a relational operator tests the
relationship between two values or expressions and
returns a boolean result (true or false)
Relational / Equality operators:
Allow comparison of the size, magnitude or equality of
data items that are the same or compatible types.
For example:
 less than ( < )…. 3 < 5 evaluates to true
 bool isLessThan = 3 < 5;
RELATIONAL / EQUALITY
OPERATORS
Operator
Meaning
True Example
False Example
<
Less Than
3<5
4 < 2 or 6 < 6
<=
Less Than OR Equal To
3 <= 4 or 3 <= 3
10 <= 5
>
Greater Than
8>7
9 > 10 or 4 > 4
>=
Greater Than OR Equal
To
5 >= 4 or 5 >= 5
5>=6
==
Equal To
20 == 20
10 == 11
!=
Not Equal To
10 != 20
20 != 20
Evaluation of either a relational or equality
operator always results to either true or false.
RELATIONAL / EQUALITY
OPERATORS
Relational Operator Priority
(<, <=, >, >=) Are below the arithmetic operator
Equality Operator Priority
( ==, !=) Are below the the relational operators
LOGICAL OPERATORS
Logical Operators ( !, &&, || ):
Allow the combination of boolean values according to
the rules of mathematical logic. Logical expressions
evaluate to a boolean result (true or false)
Not (!)
Inverts the boolean value
true becomes false or false become true
LOGICAL OPERATORS
AND (&&)
Evaluates to true only if both values are true
bool x;
bool y;
X
&&
Y
==
True
&&
True
True
True
&&
False
False
False
&&
True
False
False
&&
False
False
LOGICAL OPERATORS
OR ( || )
Evaluates to false only if both values are false
bool x;
bool y;
X
||
Y
==
True
||
True
True
True
||
False
True
False
||
True
True
False
||
False
False
OPERATOR PRECEDENCE
All operator precedence:
BOOLEAN, RELATIONAL, EQUALITY AND
LOGICAL OPERATIORS
 Example:
bool flag1, flag2, flag3;
int num1, num2;
flag1 = (98 % 13 != 98 / 13) || (2 * 5 != 10);
cout << "The truth value of variable flag1 is " << flag1 << endl;
num1 = 12 + 3 * 7;
num2 = 10 + num1 % 3;
flag2 = (num1 > num2) && (num2 < 12);
cout << "The truth value of variable flag2 is " << flag2 << endl;
flag3 = flag1 || !flag2;
cout << "The truth value of variable flag3 is " << flag3 << endl;
SELECTION
MAKING CHOICES
One-Way (choose to do or not to do)
if
Two-Way (choose to do one or the other)
if – else
conditional operator
Multiple Selection(choose to do one of many)
nested if - else
switch
ONE-WAY SELECTION
SIMPLE
 if ( RELATIONAL EXPRESSION(s) )
STATEMENT;
COMPOUND
 if ( RELATIONAL EXPRESSION(s) )
{
STATEMENT;
STATEMENT;
STATEMENT(s);
}
ONE WAY SELECTION
RULES
1. The statement(s) is/are executed if and
only if the relational expression(s)
evaluate(s) to true.
ONE WAY SELECTION
EXAMPLES:
if (current_balance > 1000)
interest = current_balance * 0.015;
if (day == 7 && hours_worked > 40)
{
ot_pay = (hours_worked – 40) * pay_rate * 2;
total_pay = 40 * pay_rate + ot_pay;
}
ONE WAY SELECTION
EXAMPLE:
int main()
{
bool isEven;
int num;
cout << "Enter an integer ";
cin >> num;
cout << endl;
if (num > 10)
cout << num << " is greater than 10" << endl;
isEven = (num % 2 == 0);
if (isEven)
cout << num << " is an EVEN number." << endl;
if (!isEven)
cout << num << " is an ODD number." << endl;
system ("pause");
return 0;
}
TWO WAY SELECTION
SIMPLE
 if ( RELATIONAL EXPRESSION(s) )
Statement;
else
Statement;
TWO WAY SELECTION
COMPOUND
 if ( RELATIONAL EXPRESSION(s) )
{
Statement;
Statement(s);
}
else
{
Statement;
Statement(s);
}
TWO WAY SELECTION
RULES
1. First statement(s) will be executed if and only
if the evaluation of the relational
expression(s) is/are true.
2. Second statement(s) will be excuted if and
only if the evaluation of the relational
expression(s) is/are false.
TWO WAY SELECTION
EXAMPLES
char
string
float
float
employee;
state;
ot_pay, pay_rate, gross_pay;
hours_worked, tax;
Example 1:
if (state == “CO”)
tax = 0.065;
else
tax = 0.05;
TWO WAY SELECTION
EXAMPLES
Example 2:
if (employee == ‘E’ || employee == ‘S’)
gross_pay = 40 * pay_rate;
else
{
reg_pay = pay_rate * 40;
ot_pay = (hours_worked – 10) * pay_rate * 1.5;
gross_pay = reg_pay + ot_pay;
}
CONDITIONAL OPERATOR
Can Accomplish Two Way Selection Using
The Conditional Operator (?:)
expression1 ? expression2 : expression3
Example
state == “CO” ? tax = 0.065 : tax = 0.05;
Cannot Include Compound Statements