1. Chapter 3
More Flow Of Control

2. Boolean Expression < <= > >= == != ! && ||
Expression that yields bool result
Include:
6 Relational Operators
< <= > >= == !=
3 Logical Operators
! && ||

3. Boolean Expression (examples)
taxRate is over 25% and income is less than $20000 temperature is less than or equal to 75 or humidity is less than 70% age is between 21 and 60 age is 21 or 22

4. Boolean Expression (examples)
(taxRate > .25) && (income < 20000)
(temperature <= 75) || (humidity < .70)
(age >= 21) && (age <= 60)
(age == 21) || (age == 22)

5. Precedence Chart ++, --, !, - (unary minus), + (unary plus) *, /, %
+ (addition), - (subtraction)
<<, >>
<, <=, >, >=
==, !=
&& || =
Highest
Lowest

6. “Short-Circuit” Evaluation
C++ uses short circuit evaluation of logical expressions
This means logical expressions are evaluated left to right and evaluation stops as soon as the final truth value can be determined

7. Short-Circuit Example
(age > 50) && (height > 60)
When age is less than 50, evaluation can stop now because result of && is only true when both sides are true. It is already determined that the entire expression will be false.
(age > 50) || (height > 60)
When age is greater than 50, evaluation can stop now because result of is true if one side is true. It is already determined that the entire expression will be true.
However, when age is less than 50, evaluation must continue because result of the entire expression has not been determined.

8. Short-Circuit Benefits
One Boolean expression can be placed first to “guard” a potentially unsafe operation in a second Boolean expression
Time is saved in evaluation of complex expressions using operators || and &&
Optimize code by placing most telling condition first.

9. Boolean evaluation on Arithmetic Expressions
All yields either 1 or 0.
Thus, !5 = 0, !(-5) = 0, !0 = 1
In C++, these values (0 and 1) can be used arithmetically, there is no difference between a 1 derived from !5 and 1 derived from

10. Enumeration Types
Is a type whose values are defined by a list of constants type int.
enum Fruits {ORANGE, GRAPE, APPLE};

11. Enumeration Types (Notes)
Sets must be finite
Members are called enumerators- unique identifier
Members are constants of type int with default value starting from 0
Can initialize values to other than 0:
enum sizes {small, medium = 10, large = 20}
Values need not be unique
enum economy {recession = -1, depression = -2, growth = 1}
Positive or negative numbers can be associated
Can declare type and variable of that type at same time.
enum economy {recession = -1, depression = -2, growth = 1} bear ;

12. Enumeration Types (Notes)
Can use in switch as case label->integral constants
Can compare 2 different enumerated type variables by casting to int
Ex: int(jan_len) < int(false)
Cannot read or write directly because the compiler doesn’t know the rules for this type.
Why use enumerated types?
Used for program clarity
Compiler will do type checking - prevent mixing types
Use 6 for Saturday and 6 for Date allows incorrect comparison.

13. Multiway Branches When there are more than 2 options to consider
Used in:
Nested if statements
Multiway if-else statements
switch statements

14. Nested if Statements
An if statement nested inside another if statement
Indent each statement.
Use braces for clarity.

15. Dangling else in nested if statements
Compiler matches else with most recent if:
if (fuel-gauge_reading < 0.75)
if (fuel-gauge_reading <0.25)
cout<<”Fuel very low. Caution!\n”;
else
cout<<”Fuel over 3/4. Don’t stop now!\n”;
If fuel is 0.8, there is no ouput.
If fuel is 0.5, output is:
Fuel over 3/4. Don’t stop now!
Need to force compiler to match if-else correctly.

16. Dangling else in nested if statements (Solutions)
Use braces to set off inner else
if (fuel-gauge_reading < 0.75) {
if (fuel-gauge_reading <0.25)
cout<<”Fuel very low. Caution!\n”; }
else
cout <<”Fuel over 3/4. Don’t stop now!\n”;
Use null statement for else
else;

17. Multiway if-else Statements
Is another form of nested if
EXACTLY 1 of these statements will be executed.
Syntax
if ( Expression1 )
Statement1
else if ( Expression2 )
Statement2 .
else if ( ExpressionN )
StatementN
else
Statement N+1

18. Multiway if-else Statements (Notes)
Order is important.
More efficient to put most probable result first.
if (grade<70) cout<<’F’;
else if ( grade>=70) cout<<‘C’;
else if (grade>=80) cout<<‘B’;
else cout<<‘A’;
If grade is 82: C
if (grade>=90) cout<<‘A’;
else if (grade>=80) cout<<‘B’;
else if (grade>=70) cout<<‘C’
else cout<<‘F’;
If grade is 82: B

19. switch Statement Replaces the multiple alternative if statement
Work with exact value only
Computer evaluates value of grade and finds case label that matches that value.
Value must be of integral type (enum, int, char, bool)
Will not work on string, double or float.
For efficiency, put most likely options first.

20. switch Statement (Syntax)
switch ( Integral Expression ) {
case Constant1 :
Statement(s); // optional
case Constant2 : .
default : // optional }

21. switch Statement (break use)
Switch statement does action after case statement until it reaches break.
No {} needed for multiple statements.
If no break occurs in that case, execution will “fall through” and do the next case, etc. until a break is reached.
break statement returns control to next line outside switch statement.

22. switch Statement (default case)
default can be used for values not represented by any case label.
Only 1 default statement in a switch.

23. switch Statement (Example)
char finalGrade;
…. // get value for finalGrade
switch ( finalGrade ) {
case ‘A’ :
cout << “Excellence!” << endl ;
break ;
case ‘B’ :
cout << “Good!” << endl ;
case ‘C’ :
cout << “Pass!” << endl ;
case ‘D’ :
cout << “Sorry!” << endl ;
case ‘F’ :
cout << “You failed!” << endl ;
default :
cout << “It is not a grade! “ << endl ;
break ; // not needed }
finalGrade Output
A Excellence!
B Good!
C Pass!
D Sorry!
You failed!
F You failed!
Anything else It is not a grade

24. break and exit
break exits that particular control statement. Used to break out of loops, switches.
exit exits the program and can return a value EXIT_SUCCESS and EXIT_FAILURE (defined in stdlib.h) to the invoking process. (Not recommend to use in this class)

25. Blocks
A compound statement which contains local variables – denoted by braces {}.
Scope:
Visibility: Local variables can only be seen within the block. Other functions and the main program do not know they exist. Therefore, there is no conflict and other functions or programs can use variables of the same name.
Viability: Local variables are created and destroyed within the block. Saves on memory.
Block allows use of global variables and local variables.
local variable: visibility and viability is within block only!
Blocks can be nested inside other blocks.

26. Blocks (Example) float price 50.0; int num; … // Get num {
float subtotal;
subtotal = price * num; }
cout << “The total for “ << num
<< “ is “ << subtotal;
Syntax error!
float price 50.0;
int num;
… // Get num {
float subtotal;
subtotal = price * num;
cout << “The total for “ << num
<< “ is “ << subtotal; }
Legal

27. Chapter 2 Review Open Chapter 2 slides Review While and Do-While Loops
Review Increment and Decrement

28. FOR Loop Used when Syntax: Example:
for (initialize; test condition; update) {
… //loop body }
Example:
int sum = 0;
for (int i=1; i<=10; i++) //i is a local variable
sum = sum + i;

29. FOR Loop (Notes)
Can use commas to do more than 1 action in any part
for(i=1,sum=0;i<10; sum+=i++); //complete loop-no body needed
Can eliminate any part of loop
for (; Test; Action)- start missing - allows the same loop to be used for different starting points as long as initialized before used. (allows flexibility)
Ex: cin>>i;
for(; i<10; i++);
Increment in loop rather than in loop body
for (i=0; i<10; i++)
Omit everything
for (;;) // (infinite loop) {
//body of loop
if (I % 5 == 0) break; // use break to exit loop }
Accidentally eliminating loop body by placing a semicolon at the end
for (i=0; i<10; i++);
cout << i << endl; // Only 10 in the output

30. Designing Loops What kind of loop to use What do we need to know?
Must iterate at least once? Do-While
Must iterate at least never? While
Numerically increases/decreases by a set amount? While
Know exactly how many times to execute. For
Execution depends on events? While
What do we need to know?
What is the process being repeated? THE BODY
How must the process be initialized and updated? INITIALIZATION.
What is the ending condition for our loop? EXIT CONDITIONS

31. Loop For Sums and Products
Used when a value (accumulator) is to be increased/decreased by the new value.
Notes:
Accumulator for a sum must be initialized to 0.
Accumulator for a product must be initialized to nonzero.

32. Loop Ending List headed by size Count controlled loop
Input list known beforehand
Count controlled loop
number of iterations known before loops begin
Ask before iteration
Used for menus and for repeated processing
Using SENTINELS
A special value which has no valid meaning to the program and is entered by the user to terminate a loop
Running out of input
Cannot read any more input from a file
Using boolean flag
Raise flag when something happened

33. Nest Loops A loop within a loop. Example: for (int i=0; i<3; i++) {
cout << “Row# “ << i << “: ”;
for (int j=0; j<5; j++)
cout << j << “ ”;
cout << endl; }
Row# 0:
Row# 1:
Row# 2:

34. Debugging Loops
Set breakpoint at the beginning of the loop. Check the LCV value when this breakpoint is hit.
Set breakpoint at the first line of the loop body. Check if the execution stops at this breakpoint.
Repeat 2 above steps would help to find problem with the loops