1. Chapter 7 Conditional Statements

2. 7.1 Conditional Expressions
Condition – any expression that evaluates to true/false value
<expr1> <relational_operator> <expr2>
Relational operators are BINARY
X < Y == a+b q+1 != s*2

3. 7.1.1 Relational Operators Relational Operator Description ==
Equality (be sure to use two equal signs) * !=
Inequality
<
Less than
>
Greater than
<=
Less than or equal to
>=
Greater than or equal to
* Single equal sign (=) is an assignment / does NOT compare values

4. 7.1.1 Relational Operators const int CONST_iEXP = 9;
int iexp1 = 0, iexp2 = 5;
float fexp = 9.0;
char cexp = 'a';
bool result = true;
result = iexp1 == 0; // true
result = iexp2 >= iexp1; // true
result = iexp1 > CONST_iEXP; // false
result = fexp == CONST_iEXP; // true
result = cexp <= iexp1; // false
result = iexp1 != iexp2; // true
result = cexp == 'a'; // true

5. 7.1.1 Relational Operators
// ILLEGAL OR MALFORMED CONDITIONS ----
result = 3 < X < Y;
// Malformed condition. What does it mean?
// 3 < X and X < Y ???
// 3 < X or X < Y ???
cexp == "a";
// Illegal. Attempting to compare a character // to a string literal.

6. 7.1.2 Logical Operators Logical operators - combine bool expressions
or: x || y (binary operator)
false only when both operands are false
and: x && y (binary operator)
true only when both operands are true
not: !x (unary operator)
false when operand is true; otherwise true.

7. 7.1.2 Logical Operators
Truth table - displays Boolean results produced when the operator is applied to specified operands
Logical AND and OR truth table
Condition c1
Condition c2
c1 && c2
c1 || c2
true
false

8. 7.1.2 Logical Operators Logical NOT truth table ! (not) && (and)
Order of precedence
! (not)
&& (and)
|| (or)
Condition c !c
true
false

9. 7.1.2 Logical Operators Misc Information:
Parentheses change the precedence
Parentheses can help clarify complicated conditions
Short-circuit evaluation - once the outcome of condition can be determined, evaluation ends

10. 7.1.2 Logical Operators Various logical operators
int iexp1 = 0, iexp2 = 5;
float fexp = 9.0;
char cexp = 'a';
const int CONST_iEXP = 9;
bool result;
result = iexp1 < iexp2 && fexp == 9.0;
result = iexp1 > CONST_iEXP || fexp == 9.0; // true
result = !(fexp == 9.0 || iexp1 > CONST_iEXP);// false
// Short-Circuit Evaluation
result = fexp == 9.0 || iexp1 > CONST_iEXP; // true

11. 7.2 The if Statement
Selects actions to be taken only when a specific condition is satisfied
Syntax: if ( <condition> )
<action>
Example: if ( N % 2 == 1)
cout << N << “ is ODD” << endl;

12. 7.2 if (<condition>) <action>
<condition> - a valid expression that can be interpreted as a TRUE/FALSE value
Relational expression (e.g., x <= 2)
Logical expression ( x>5 && y != 2)
Integer-valued expression: 0=false; otherwise true.
<action> - a valid C++ statement or block
Single statement terminated with semicolon
Compound statement (block) enclosed in set braces { }
if (Age > 21) if (Income > 24000)
Sell_Beer = true; {
SSTax = 0.05 * Income;
FedTax = * Income; }

13. 7.2 The if Statement if (condition) statement; // Example 1
if ( test >= 80 && test < 90 )
cout << "You have earned a B" << endl;
// Example 2 – relational expression/compound statement.
if ( test >= 90 ) {
cout << "You have earned an A" << endl;
cout << "Excellent work!" << endl; }
// Example 3 – logical expression/compound statement.
if ( test >= 70 && test < 80 )
cout << "You have earned a C" << endl;

14. 7.2.1 The else Statement Optional part of an if statement
Can’t stand alone
Must be associated with an open if
if ( <condition> )
<action 1> // Consequence (true-part)
else
<action 2> // Alternative (false-part)
Means: “otherwise”, “catch-all”, “none of the above”

15. 7.2.1 The else Statement else <action> // consequence.
no condition or expression associated with it
relies on the value of the condition associated with the previous if (or chain of ifs)
executes action(s) only if the previous condition (or chain of ifs) is false
if more than one statement, the action must be enclosed in curly braces

16. 7.2.1 The if-else Statement else Example if ( grade >= 60 )
pass = true;
else {
pass = false;
cout << "Hope you do better next time" << endl; }

17. 7.2.1 Multiple alternative if
The alternative of an if is another decision:
if ( avg >= 90 )
cout << “Grade = A" << endl;
else
if ( avg >= 80 )
cout << "B" << endl;
NOTE indentation.
else if ( avg >= 80 )

18. 7.2.1 Selecting from multiple alternatives
Only ONE action is selected from a chain of decisions.
if ( Avg >= 90 )
Grade = ‘A’;
else if ( Avg >= 80 )
Grade = ‘B’;
else if ( Avg >= 70)
Grade = ‘C’;
else if ( Avg >= 60)
Grade = ‘D’;
else // Optional
Grade = ‘F’;
NOTE: The construct terminates when a choice is made.
QUESTIONS: # of decisions needed to assign A? C? F?

19. 7.2.1 Sequence of if statements
Inefficient: how many decisions for A, C, F?
if ( avg >= 90 )
cout << "A" << endl;
if ( avg >= 80 && avg < 90 )
cout << "B" << endl;
if ( avg >= 70 && avg < 80 )
cout << "C" << endl;
if ( avg >= 60 && avg < 70 )
cout << "D" << endl;
if ( avg < 60 )
cout << "F" << endl;

20. 7.2.1 Multiple-alternative chain of if
Mutual exclusion: result can be only one of the choices
if ( avg >= 90 )
cout << "A" << endl;
else if ( avg >= 80 )
cout << "B" << endl;
else if ( avg >= 70 )
cout << "C" << endl;
else if ( avg >= 60 )
cout << "D" << endl;
else
cout << "F" << endl; 90 80 70 60

21. 7.2.1 Multiple alternative if chain
Notes:
Each condition is tried until one is satisfied (i.e., value is true)
The matching consequence is executed
The decision process terminates the

22. 7.2.1 The Nested if construct
Nested  the consequence is itself a decision.
if ( gpa >= 3.75 )
if ( credits > 25 )
if ( money < )
{ scholarship = 5000;
cout << "Way to go!" << endl; }
else
scholarship = 2000;
scholarship = 1000;
{ scholarship = 0;
cout << "You're on your own." << endl;

23. 7.3 Variable Scope Scope of a variable – determines:
What code can access or change the variable
How long the variable exists or lives

24. 7.3 Variable Scope
Below, var_a and var_b defined within the scope of the block
Both accessible within the block where defined
Final line generates an error message - var_b is not defined {
int var_a = 5, var_b = 10;
var_a++;
cout << "var_a: " << var_a << endl; }
cout << "var_b: " << var_b; // Error: undeclared // identifier var_b

25. 7.3 Variable Scope
Local scope – variables or constants declared within braces

26. 7.3 Variable Scope
Constant PI and variable global_area - physically declared outside of function - placed at the global level
#include <iostream>
using std::cout;
using std::endl;
#include <cmath> // Needed for pow
const float PI = F; // global scope
float global_area = 0; // global scope
int main()
{ float radius = 5; // local scope
global_area = static_cast<float>( PI * pow( radius, 2 ) );
cout << global_area << " sq. in." << endl;
return 0; }
// Output
sq. in.

27. 7.3 Variable Scope
Any code within the file can access PI or global_area
#include <iostream>
using std::cout;
using std::endl;
#include <cmath> // Needed for pow
const float PI = F; // global scope
float global_area = 0; // global scope
int main()
{ float radius = 5; // local scope
global_area = static_cast<float>(PI * pow(radius, 2));
cout << global_area << " sq. in." << endl;
return 0; }
// Output
sq. in.

28. 7.3 Variable Scope Global variables - automatically initialized to 0
Avoid global variables (i.e., global_area)
#include <iostream>
using std::cout;
using std::endl;
#include <cmath> // Needed for pow
const float PI = F; // global scope
float global_area = 0; // global scope
int main()
{ float radius = 5; // local scope
global_area = static_cast<float>(PI * pow(radius, 2));
cout << global_area << " sq. in." << endl;
return 0; }
// Output
sq. in.

29. 7.4 The switch Statement
switch statement - another form of conditional statement
Also called a selection statement
Checks only for equality and only for one variable

30. 7.4 The switch Statement
Works well for checking a variable for limited set of values
Only works with ordinal data types
Ordinal data types - can be translated into an integer to provide a finite, known, number set
Examples include int, bool, char, and long

31. 7.4 The switch Statement General form of the switch statement:
switch( <variable> )
{ // Required
case <literal or const 1>:
<action 1>
break;
case <literal or const 2>:
<action 2>
...
default: // Optional
<default action>
}// Required
When first line is encountered, value of the variable determined
Execution jumps to the case which corresponds to the value of the variable being examined
Execution continues until either a break statement is encountered or to the end of switch

32. 7.4 The switch Statement
break statement - stops execution of the control structure prematurely
Stops multiple case statements from being executed
Many believe poor programming to use outside the context of the switch statement

33. 7.4 The switch Statement
default statement - executed if value of the variable doesn’t match any of previous cases
Type of catch all or “case else”
Technically can use the default case in any position
Should physically be the last one in the switch statement

34. 7.4 The switch Statement int menu_item = 0; ... switch ( menu_item ) {
case 1: // Using literal values
cout << "You have chosen option 1." << endl;
break;
case 2:
cout << "You have chosen option 2." << endl;
case 3:
cout << "You have chosen option 3." << endl;
default:
cout << "Invalid menu option." << endl; }

35. 7.4 The switch Statement const short GREEN = 0;
const short YELLOW = 1;
const short RED = 2;
short light_color = GREEN;
switch ( light_color )
{ case GREEN: // Using constants
cout << "Go!" << endl;
break;
case YELLOW: // Let fall through
case RED:
cout << "Stop!";
cout << "Proceed when light is green." << endl;
default:
cout << "Power is out!" << endl; }

36. 7.4 The switch Statement char letter_grade;
cout << "Enter letter grade: ";
cin >> letter_grade;
switch ( letter_grade )
{ case 'A': // Using character literal values
cout << "Excellent!" << endl;
break;
case 'B':
cout << "Above average." << endl;
case 'C':
cout << "Average." << endl;
case 'D':
cout << "Below average." << endl;
case 'F':
cout << "Failed!" << endl;
default:
cout << "Invalid letter grade." << endl; }

37. 7.4 The switch Statement
One of the most common uses of switch statement is in menu driven programs
Student Grade Program Main Menu -
1. Enter name Enter test scores
3. Display test scores
9. Exit
Please enter your choice from the list above:

38. 7.5 Conditional Operator
Conditional operator - considered a ternary operator, meaning it has three operands
Syntax:
<condition> ? <true expression> : <false expression>

39. 7.5 Conditional Operator
One of the expressions is returned based upon the evaluation of the condition
int a = 5, b = 0;
int larger = a > b ? a : b;
cout << larger << endl;
// Output 5

40. 7.5 Conditional Operator
Equivalent if statement to code on previous page
int a = 5, b = 0;
int larger;
if ( a > b )
larger = a;
else
larger = b;

41. 7.5 Conditional Operator More challenging conditional operator example
short hour = 9, minute = 10, second = 5;
cout << (hour < 10 ? "0" : "") << hour << ":"
<< (minute < 10 ? "0" : "") << minute << ":"
<< (second < 10 ? "0" : "") << second << endl;
// Output
09:10:05
Empty quotes above tell cout to print nothing if the condition is false (i.e. hour is 10 or greater)