1. Chapter 4 :
Control Construct

2. Key Concepts: logical values and operation true tables bool type
relational operators
short-circuit evaluation
if-else statement
switch statement
break statement
enum statement
for construct
while construct
do construct
infinite loops
invariants

3. Boolean Algebra
Logical expressions have the one of two values - true or false
A rectangle has three sides
The instructor has a pleasant smile
The branch of mathematics is called Boolean algebra
Developed by the British mathematician George Boole
in the 19th century
Three key logical operators
And Or
Not

4. Boolean Algebra P Q P and Q True table of logical “and”
Truth tables
Lists all combinations of operand values and the result of the operation for each combination
P Q P and Q
false false false
false true false
true false false
true true true
True table of logical “and”

5. Boolean Algebra True table of logical “or” P Q P or Q
Truth tables
Lists all combinations of operand values and the result of the operation for each combination
P Q P or Q
false false false
false true true
true false true
true true true
True table of logical “or”

6. Boolean Algebra P not P false true true false
Truth tables
Lists all combinations of operand values and the result of the operation for each combination
P not P
false true
true false
True table of logical “not”

7. Boolean Algebra
Can create complex logical expressions by combining simple logical expressions
Example
not (P and Q)
A truth table can be used to determine when a logical expression is true
P Q P and Q not(P and Q)
false false
false true
true false
true true
false
true
false
true
false
true
true
false

8. A Boolean Type C++ contains a type named bool
Type bool has two symbolic constants
true
false
Boolean operators
The and operator is &&
The or operator is ||
The not operator is !
Warning
& and | are also operators so be careful what you type

9. A Boolean Type Example logical expressions
bool P = true; bool Q = false; bool R = true; bool S = (P && Q); bool T = ((!Q) || R); bool U = !(R && (!Q));

10. Relational Operators Equality operators == != Examples int i = 32;
int k = 45;
bool q = (i == k);
bool r = (i != k);

11. Relational Operators Ordering operators < > >= <= Examples
int i = 5;
int k = 12;
bool p = (i < 10);
bool q = (k > i);
bool r = (i >= k);
bool s = (k <= 12);

12. Operator Precedence Revisited
Precedence of operators (from highest to lowest)
Parentheses (), []
Unary operators !, +, -, ++, --, *, &, …
Multiplicative operators *, /, %
Additive operators , -
Relational ordering >, >=, <, <=
Relational equality ==, !=
Logical and &&
Logical or ||
Assignment =, +=, -=, *=, /=

13. Operator Precedence Revisited
Consider
5 * == 13 && 12 < 19 || !false == 5 < 24
Yuck! Do not write expressions like this!

14. Operator Precedence Revisited
Consider
5 * == 13 && 12 < 19 || !false == 5 < 24
However, for your information it is equivalent to
5 * == 13 && 12 < 19 || !false == 5 < 24
( )
( )
( )
( )
( )
( )
( )
( )

15. Operator Precedence Revisited
Consider
5 * == 13 && 12 < 19 || !false == 5 < 24
However, for your information it is equivalent to
((((5 *15) + 4) == 13) && (12 < 19)) || ((!false) == (5 < 24))
Short-circuit evaluation
bool b = (i != 0 ) && ((j/i) < 5);

16. Three Basic Constructs
In structural programming paradigm, any complex computing can be expressed by the statements of only three basic constructs
1. Sequence construct
2. Conditional construct
3. Iteration construct

17. Three Basic Constructs
Sequence construct A B C

18. Three Basic Constructs
Conditional construct
Condition A B
Yes No
Condition A
Yes No

19. Three Basic Constructs
Iteration construct
Condition A
Yes No
Condition A
Yes No

20. Basic Flow Diagram Symbols
Connections
Start/End
Procedure
Condition
Input/Output

21. Flow Diagram Example Start a < b Input a, b, c min = a min = b YesNo
c < min
min = c
Output min
End
Yes No

22. Conditional Constructs
Provide
Ability to control whether a statement list is executed
Two constructs
If statement if
if-else
if-else-if
Switch statement
switch - case

23. The Basic if Statement Expression Action true false if (Expression)
Syntax
If the Expression is true then execute Action
Action is either a single statement or a group of statements within braces

24. Example if (iValue < 0) { iValue = -iValue; }
Is our number negative?
iValue < 0
iValue = -iValue
true
false
If Value is less than
zero then we need
to update its value
to that of its
additive inverse
If Value is not less
than zero then our
number is fine as is
Our number is
now definitely
nonnegative

25. Sorting Two Numbers cout << "Enter two integers: "; int iValue1;
cin >> iValue1 >> iValue2;
if (iValue1 > iValue2) {
int iTemp = iValue1;
iValue1 = iValue2;
iValue2 = iTemp; }
cout << "The input in sorted order: "
<< iValue1 << " " << iValue2 << endl;

26. Semantics Are the numbers out of order Rearrange value1
iValue2 < iValue1
int iTemp = iValue1
iValue1 = iValue2
iValue2 = iTemp
true
false
Are the numbers
out of order
Rearrange value1
and value2 to put their values in the proper order
The numbers were
rearranged into the
proper order
The numbers were
initially in order
The numbers are in order

27. What is the Output? int m = 10; int n = 5; if (m < n) ++m; ++n;
cout << " m = " << m << " n = " n << endl;

28. The if-else Statement Syntax if (Expression) Action1 else Action2
true
false
If Expression is true then execute Action1 otherwise execute Action2
if (v == 0) {
cout << "v is 0";
} else
{ cout << "v is not 0"; }

29. Example: Finding the Max
cout << "Enter two integers: ";
int iValue1;
int iValue2;
cin >> iValue1 >> iValue2;
int iMax;
if (iValue1 < iValue2) {
iMax = iValue2; }
else
iMax = iValue1;
cout << "Maximum of inputs is: " << iMax << endl;

30. Finding the Max Is Value2 larger than Value1 Yes, it is . So Value2 is
larger than Value1. In
this case, Max is set
to Value2
iValue1 < iValue2
Max = iValue2
Max = iValue1
true
false
No, its not. So Value1
is at least as large as
Value2. In this case,
Max is set to Value1
Either case, Max is set
correctly

31. Selection
It is often the case that depending upon the value of an expression we want to perform a particular action
Two major ways of accomplishing this choice
if-else-if statement
if-else statements “glued” together
switch statement
An advanced construct

32. An if-else-if Statement
if ( nbr < 0 )
{ cout << nbr << " is negative" << endl; }
else if ( nbr > 0 )
{ cout << nbr << " is positive" << endl;
else
{ cout << nbr << " is zero" << endl;

33. A switch Statement switch( SwitchExpression ) { case CaseExpression1 :
Action1;
break;
case CaseExpression2 :
Action2;
......
case CaseExpressionN :
ActionN;
default: Default action; }
The case expression must be
constant integral expression
Actions are either a single statement or a group of statements

34. A switch Statement Example: switch (ch) { case 'a': case 'A':
case 'e': case 'E':
case 'i': case 'I':
case 'o': case 'O':
case 'u': case 'U': cout << ch << " is a vowel" << endl;
break;
default: cout << ch << " is not a vowel" << endl; }

35. cout << "Enter simple expression: ";
int iLeft;
int iRight;
char chOperator;
cin >> iLeft >> chOperator >> iRight;
cout << iLeft << " " << chOperator << " " << iRight << " = ";
switch (chOperator) {
case '+' :
cout << iLeft + iRight << endl; break;
case '-' :
cout << iLeft - iRight << endl; break;
case '*' :
cout << iLeft * iRight << endl; break;
case '/' :
cout << iLeft / iRight << endl; break;
default: cout << "Illegal operation" << endl; }

36. enum statement enum TypeName … SymbolicConstantN [ = n ]
C++ provides enum statement to define a collection of related symbolic constant
It can also be used to define a
programmer-defined types
enum TypeName {
SymbolicConstant1 [ = i ] ,
SymbolicConstant2 [ = j ] , …
SymbolicConstantN [ = n ] };
Note:
1. Here […] indicates the options
2. i, j and n must be integers
If the SymbolicConstant is not assigned a integer value, the first
will have 0, and the next will be increment automatically.

37. Example of enum type enum MONTHS_OF_YEAR { January = 1, February,
March , April ,
May , June ,
July , August ,
September , October ,
November , December };
enum DAY_OF_WEEK {
Monday = 1, Tuesday ,
Wednesday , Thursday,
Friday , Saturday,
Sunday };
enum COLORS {
Black, Red, Green, Blue, Yellow, Pink, White };

38. Example of enum type MONTHS_OF_YEAR emMonth = January;
DAY_OF_WEEK emDayOfWeek = Thursday;
COLORS emColor = Green;
int iDay = 30;
switch(emMonth) {
case January:
iDay = 31;
break;
case February:
iDay = 28;
default: }

39. Iterative Constructs
Mechanisms for deciding under what conditions an action should be repeated

40. Averaging

41. Determining Average Magnitude
Suppose we want to calculate the average apparent brightness of a list of five star magnitude values
Can we do it
Yes, it would be easy
Suppose we want to calculate the average apparent brightness of a list of 8,479 stars visible from earth
Yes, but it would be gruesome without the use of iteration
Suppose we want to calculate the average apparent brightness of a list of five star magnitude values
Can we do it?
Yes, it would be easy

42. C++ Iterative Constructs
Three constructs
while statement
for statement
do-while statement
The while statement
Syntax
Logical expression that
Determines whether the
action is to be executed
while
( Expression ) {
Action; }
Action to be iteratively
performed until logical
expression is false

43. while Semantics Expression is evaluated at the start of each
iteration of the
loop
Expression
Action
true
false
If Expression is
true, Action is
executed.
If Expression is
false, program
Execution
continues with
next statement

44. // Computing an average
int iListSize = 4;
int iProcessedNbr = 0;
double dSum = 0.0;
while (iProcessedNbr < iListSize) {
double dValue;
cin >> dValue;
dSum += dValue;
++iProcessedNbr; }
double dAverage = dSum / iProcessedNbr;
cout << "Average: " << dAverage << endl;

45. Better Way of Averaging
// Computing an average
int iProcessedNbr = 0;
double dSum = 0.0;
double dValue;
while ( cin >> dValue ) {
sum += dValue;
++iProcessedNbr; }
double dAverage = dSum / iProcessedNbr ;
cout << "Average: " << dAverage << endl;
The value of the input operation corresponds to true only if a successful extraction was made
What if list is empty?

46. Even Better Way of Averaging
// Computing an average
int iProcessedNbr = 0;
double dSum = 0.0;
double dValue;
while ( cin >> dValue ) {
dSum += dValue;
++iProcessedNbr; }
if ( iProcessedNbr > 0 )
double dAverage = dSum / iProcessedNbr ;
cout << "Average: " << dAverage << endl;
else
cout << "No list to average" << endl;

47. const int TABLE_SIZE = 20;
int i = 0;
long lEntry = 1;
cout << "i" << "\t\t" << "2 ** i" << endl;
while (i < TABLE_SIZE )
{ cout << i << "\t\t" << lEntry << endl; lEntry = 2 * lEntry; ++i; }
//Power of Two Table

48. The for Statement for (ForInit ; ForExpression; PostExpression) {
Syntax
for (ForInit ; ForExpression; PostExpression) {
Action; }
Example
for (int i = 0; i < 3; ++i)
{ cout << "i is " << i << endl; }

49. ForInit ForExpr false true Action PostExpr Evaluated once at
the beginning of the
for statements's
execution
ForExpr
Action
true
false
ForInit
PostExpr
The ForExpr is
evaluated at the
start of each
iteration of the
loop
If ForExpr is
true, Action is
executed
After the Action
has completed,
the PostExpression
is evaluated
If ForExpr is
false, program
execution
continues with
next statement
After evaluating the
PostExpression, the next
iteration of the loop starts

50. Table Revisiting //Power of Two Table const int TABLE_SIZE = 20;
long lEntry = 1;
cout << "i" << "\t\t" << "2**i" << endl;
for (int i = 0; i <= TABLE_SIZE; ++i)
{ cout << i << "\t\t" << lEntry << endl; lEntry *= 2; }

51. Table Revisiting //Power of Two Table const int TABLE_SIZE = 20;
long lEntry = 1;
cout << "i" << "\t\t" << "2**i" << endl;
for (int i = 0; i <= TABLE_SIZE; ++i)
{ cout << i << "\t\t" << lEntry << endl; lEntry *= 2; }
cout << "i is" << i << endl; // illegal
The scope of i is limited to the loop!

52. Fibonacci sequence The first 8 number of Fibonacci sequence:
1, 1, 2, 3, 5, 8, 13, 21 …

53. Displaying a Diagonal SimpleWindow W("One diagonal", 5.5, 2.25);
W.Open();
for (int j = 1; j <= 3; ++j) {
float x = j * ;
float y = j * ;
float fSide = 0.4;
RectangleShape S(W, x, y, Blue, fSide, fSide);
S.Draw(); }

54. Displaying Three Diagonals
SimpleWindow W("Three diagonals", 6.5, 2.25);
W.Open();
for (int i = 1; i <= 3; ++i) {
for (int j = 1; j <= 3; ++j)
float x = i j * ;
float y = j * ;
float Side = 0.4;
RectangleShape S(W, x, y, Blue, Side, Side);
S.Draw(); }

55. int Counter1 = 0; int Counter2 = 0; int Counter3 = 0; int Counter4 = 0; int Counter5 = 0; ++Counter1;
for (int i = 1; i <= 10; ++i) { ++Counter2; for (int j = 1; j <= 20; ++j) { Counter3; }
++Counter4; }
++Counter5;
cout << Counter1 << " " << Counter2 << " "
<< Counter3 << " " << Counter4 << " "
<< Counter5 << endl;

56. for into while for (ForInit ; ForExpression; PostExpression) { Action;}
ForInit;
while( ForExpression ) {
Action;
PostExpression; }

57. Counting Characters int iNbrOfNonBlanks = 0; int iNbrOfUpperCase = 0;
char c;
while (cin >> c) {
++iNbrOfNonBlanks;
if ((c >= 'A') && (c <= 'Z'))
{ ++iNbrOfUpperCase; }
cout << "Nonblank characters: "
<< iNbrOfNonBlanks
<< endl << "Uppercase characters: "
<< iNbrOfUpperCase << endl;
Counting Characters
Only extracts nonblank characters

58. Counting All Characters
int iNbrOfChars = 0;
int iNbrOfLines = 0;
char c;
while ( cin.get(c) )
{ ++ iNbrOfChas; if (c == '\n')
{ ++ iNbrOfLines; }
cout << "Characters: " << iNbrOfChars
<< endl << "Lines: " << iNbrOfLines
<< endl;
Counting All Characters
Extracts all characters

59. File Processing #include <iostream> #include <fstream>
using namespace std;
int main() {
ifstream fin("mydata.txt");
int iValuesProcessed = 0;
float fValueSum = 0;
float fValue;
while ( fin >> fValue )
fValueSum += fValue;
++iValuesProcessed; }
if (iValuesProcessed > 0)
ofstream fout("average.txt");
float fAverage = fValueSum / iValuesProcessed;
fout << "Average: " << fAverage << endl;
return 0;
else
cerr << "No list to average" << endl;
return 1;
File Processing

60. The Do-While Statement
Syntax do {
Action;
} while (Expression)
Action
true
false
Expression
Semantics
Execute Action
If Expression is true then execute Action again
Repeat this process until Expression evaluates to false
Action is either a single statement or a group of statements within braces

61. Waiting for a Proper Reply
char chReply; do {
cout << "Decision (y, n): ";
if (cin >> chReply)
chReply = tolower(chReply);
else
chReply = 'n';
} while ((chReply != 'y') && (chReply != 'n'));

62. Iteration Do’s Key Points
Make sure there is a statement that will eventually terminate the iteration criterion
The loop must stop!
Make sure that initialization of loop counters or iterators is properly performed
Have a clear purpose for the loop
Document the purpose of the loop
Document how the body of the loop advances the purpose of the loop

63. Home works Exercises 4.1 ~ 4.3 Exercises 4.12~4.14

64. End of Chapter 4