Chapter 3 Decision Structures and Boolean Logic
ITP 134 C++ Study Guide
Chapter 3 Decision Structures and Boolean Logic
Instructions: Use this Study Guide to help you understand the important points of this chapter. See
the book for lots of great programming examples. Important concepts, keywords, statements and
functions are shown in emphasized font.
Code syntax and examples are shown in code font.
Games & Graphics in C++
2nd edition by Tony Gaddis
3.1 Control Structures
CONCEPT: Control structures affect the order in which
statements execute. There are 3 main types of control
structures, sequence, selection, and repetition. (pg 87)
1. Sequence – set of statements that execute in
the order that they appear
2. Selection (also called decision) – structure used
to create a program with more than one path of
execution (pg 89)
3. Repetition (also called loop or iteration ) –
structure used to repeat the same set of
statements a number of times (pg 89)
Combine Control Structures (Not in book, from
CSC 200 class)
 Each control structure has a single entry and a
single exit point.
 Two ways to combine control structures, stack
or nest. See Section 3.4 for nested structures.
 Figure 3.8 on page 102 shows example of
stacked structures.
 Figure 3.9 on page 103 shows example of
nested structures.
Flowchart Symbols (from CSC 200 class)
Terminal symbol. Starts and ends a program. Add Start at the beginning and End at the end.
Use the function name in this symbol to start functions.
Decision symbol. Used to ask a question. Put the question inside the symbol.
Process symbol. Used for statements inside a block or sequence. Put the pseudocode
statement inside the symbol.
Connector symbol. Used to connect flowcharts on the same page. Put A, B, C etc inside the
symbol.
Off page symbol. Used to connect flowcharts on 2 pages. Put the page number inside the
symbol.
Data symbol. Use for input or output.
ITP 134 – Mrs. Eaton
Chapter 3 Study Guide – 2nd Edition
Page 1
Chapter 3 Decision Structures and Boolean Logic
/* executes if false */
statements;
3.2 Writing a Decision Structure with the
if Statement
CONCEPT: The if statement is used to create a decision
structure, which allows a program to have more than
one path of execution.
The if statement causes one or more statement to
execute only when a Boolean expression is true.
If statement (general form) is: (see page 90) Use for
true/false type questions.
if (expression)
{
statement;
statement;
statement;
}
In the Spotlight: Auto Repair Payroll
 Create a program to calculate hourly rate and
overtime (pg 100-101)
3.4 Nested Decision Structures and the ifelse-if Statement
CONCEPT: To test more than one condition, a decision
structure can be nested inside another decision
structure. (pg 101)
See Figure 3-10 Flowchart for Nested if statements on
page 104 for good examples.
Boolean Expressions and Relational Operators
The value of a Boolean expression can be either true or
false. Boolean algebra is named after the English
mathematician George Boole. (pg 92)
Relational Operators: (See table 3-1 on page 92)
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}
Programming Style and Nested Decision
Structure
 See page 106 at top for wrong way to indent
code.
 See Figure 3-11 Alignment of if and else clauses
(pg 106) for to the professional way to indent
code.
The if-else-if Statement
Nested if statements can become complex. C++
provides a special if-else-if statement which makes the
logic easier to write. Use as an alternative to nested if
statements. (Page 109) Here is the logic:
> greater than;
< less than
>= greater or equal
<= less or equal
== equal to
!= not equal
if (expression1)
{
/* executes if true */
statements;
}
else if (expression2)
{
//executes expression2 true
statements;
}
// insert more else if clauses
else
{
// executes expression1 false
statements;
}
Putting it All Together
See Program 3-1, TestAverage.cpp for an example of if
statement program. (pg 96)
3.3 The if-else Statement
CONCEPT: An if-else statement will execute one block of
statements if its Boolean expression is true, or another
block if the Boolean expression is false.
If-else statement (general form) is:
Use for true/false type questions. (See page 98)
if (expression)
{
/* executes if true */
statements;
}
else
{
ITP 134 – Mrs. Eaton
3.5 Logical Operators
CONCEPT: The logical AND operator (&&) and the
logical OR operator (||) allow you to connect multiple
Boolean expressions to create a compound expression.
Chapter 3 Study Guide – 2nd Edition
Page 2
Chapter 3 Decision Structures and Boolean Logic
The logical NOT operator (!) reverses the truth of a
Boolean expression. (page 112)
Truth Tables for Boolean Expressions
Not in Book
AND logical operator is true only when both are true.
A
B
A && B
F
F
F
F
T
F
T
F
F
T
T
T
OR logical operator false only when both are false.
A
B
A || B
F
F
F
F
T
T
T
F
T
T
T
T
NOT logical operator reverses Boolean value
A
T
F
!A
F
T
Precedence of Logical Operators
NOT has a higher precedence that the relational
operators. AND and OR have a lower precedence than
the relational operators. (page 115)
3.6 The switch Statement
CONCEPT: The switch statement lets the value of a
variable or an expression determine which path of
execution the program will take. (page 116)
The switch statement is used for multiple choice type
decisions. See Figure 3-213 (page 117) for a logical view
of a switch statement.
The general syntax for a switch statement is
switch(x)
{
case value1:
// executes when x=value1
statements;
break;
case value2:
// executes when x=value2
statements;
break;
// insert other case statements
default:
statements;
}
3.7 Bool Variables
CONCEPT: A bool (Boolean) variable can store the
values true and false. Variables of the bool data type
are commonly used as flags which indicate whether
specific conditions exist.
For example,
// flag if more than 5000 pts
bool grandMaster;
if (points > 5000)
{
grandMaster = true;
}
else
{
grandMaster = false;
}
3.8 Comparing Strings
CONCEPT: C++ allows you to compare strings. This
allows you to create decision structures that test the
value of a string. (pg 123)
Important points about switch statements (page 118)
a) X value must be an integer or an expression
that gives an integer value.
b) Value that follows the case keyword must be an
integer literal or constant. It cannot be a
variable.
c) The break clause is optional, but if you do not
use it the next case clause will also execute.
d) The default clause is optional, but it a smart
exception handling statement.
Chapter 3 Program Examples
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e) Since default clause it at the end, it does not
need a break statement.
ITP 134 – Mrs. Eaton
Chapter 3 Study Guide – 2nd Edition
Program 3-1 TestAverage.cpp (pages 95-97)
Program 3-2 AutoRepairPayroll.cpp (page 100101)
Program 3-3 LoanQualifier.cpp (page 104-105)
Program 3-4 Grader.cpp (page 107-109)
Program 3-5 Grader2.cpp (page 110-111)
Program 3-6 SwitchExample.cpp (page 119-121)
Program 3-7 CompareStrings.cpp (Page 123124)
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