1. COMS 261 Computer Science I
Title: C++ Fundamentals
Date: September 17, 2004
Lecture Number: 12

2. Announcements Project 1 Exam 1 Due 9/24/04 (next Friday)
9/22/04 (next Wednesday)

3. Review Boolean Algebra Boolean Type Relational Operators
Operator Precedence Revisited
Conditional Constructs

4. Outline
Conditional Constructs
Iterative Constructs

5. Operator Precedence Revisited
Consider
5 * == 13 && 12 < 19 || !false == 5 < 24
Is equivalent to
((((5 *15) + 4) == 13) && (12 < 19)) || (!false) == (5 < 24))

6. Conditional Constructs
Provide
Ability to control whether a statement list is executed
Two constructs
If statement if
if-else
if-else-if
Switch statement
Left for reading

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

8. Example
if (Value < 0) {
Value = -Value; }

9. Sorting Two Numbers cout << "Enter two integers: "; int value1;
cin >> value1 >> value2;
if (value1 > value2) {
int rememberValue1 = value1;
value1 = value2;
value2 = rememberValue1; }
cout << "The input in sorted order: "
<< value1 << " " << value2 << endl;

10. Semantics

11. The If-Else Statement Syntax if (Expression) Action1 else Action2
If Expression is true then execute Action1 otherwise execute Action2
if (v == 0) {
cout << "v is 0";
} else { cout << "v is not 0"; }
Check out the indentation!
Expression
Action1
Action2
true
false

12. Finding the Max cout << "Enter two integers: "; int value1;
cin >> value1 >> value2;
int max;
if (value1 < value2) {
max = value2;
} else {
max = value1; }
cout << "Maximum of inputs is: " << max << endl;

13. Finding the Max

14. 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

15. 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; }

16. A Switch Statement 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; }

17. Example cout << "Enter simple expression: "; int left;
int right;
char operator;
cin >> left >> operator >> right;
cout << left << " " << operator << " " << right << " = ";
switch (Operator) {
case '+' : cout << left + right << endl; break;
case '-' : cout << left - right << endl; break;
case '*' : cout << left * right << endl; break;
case '/' : cout << left / right << endl; break;
default: cout << "Illegal operation" << endl; }

18. Determining Average Magnitude
Calculate the average brightness of a list of five star magnitude values
Can we do it?
Yes, it would be easy
Calculate the average brightness of a list of 8,479 stars visible from earth
Can we do it
Yes, but it would be tedious without the use of iteration

19. C++ Iterative Constructs
Three constructs
while statement
for statement
do-while statement

20. While Syntax

21. While Semantics

22. Computing an Average int listSize = 4; int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;

23. Execution Trace Suppose input contains: 1 5 3 1 6 int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;

24. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;

25. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;

26. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum

27. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum

28. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum
value --

29. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum
value --

30. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum
value 1

31. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 1
value 1

32. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 1
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 1
value 1

33. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 1
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 1
value 1

34. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 1
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 1
value 1

35. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 1
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 1
value 1

36. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 1
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 1
value 5

37. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 1
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 1
value 5

38. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 1
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 6
value 5

39. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 1
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 6
value 5

40. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 2
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 6
value 5

41. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 2
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 6
value 5

42. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 2
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 6
value 5

43. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 2
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 6
value 3

44. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 2
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 9
value 3

45. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 3
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 9
value 3

46. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 3
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 9
value 3

47. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 3
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 9
value 3

48. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 3
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 9
value 1

49. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 3
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 10
value 1

50. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 4
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 10
value 1

51. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 4
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
sum 10
value 1

52. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 4
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed;
cout << "Average: " << average << endl;
sum 10
value 1
average
2.5

53. Execution Trace Suppose input contains: 1 5 3 1 6 listSize 4
numberProcessed 4
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed;
cout << "Average: " << average << endl;
sum 10
value 1
average
2.5

54. Stays in stream until extracted
Execution Trace
Suppose input contains:
Stays in stream until extracted
int listSize = 4;
int numberProcessed = 0;
double sum = 0;
while (numberProcessed < listSize) {
double value;
cin >> value;
sum += value;
++numberProcessed; }
double average = sum / numberProcessed;
cout << "Average: " << average << endl;

55. Even Better Way of Averaging
int numberProcessed = 0;
double sum = 0;
double value;
while (cin >> value) {
sum += value;
++numberProcessed; }
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
The value of the extraction operation corresponds to true only if a successful extraction was made
What if list is empty?

56. Even Better Way of Averaging
int numberProcessed = 0;
double sum = 0;
double value;
while (cin >> value) {
sum += value;
++numberProcessed; }
if (numberProcessed > 0) {
double average = sum / numberProcessed ;
cout << "Average: " << average << endl;
} else {
cout << "No list to average" << endl;

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

59. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl; i

60. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl; i

61. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0 i

62. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0 i

63. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0 i 1

64. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl; i 1

65. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1 i 1

66. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1 i 1

67. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1 i 2

68. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1 i 2

69. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1
i is 2 i 2

70. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1
i is 2 i 2

71. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1
i is 2 i 3

72. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1
i is 2 i 3

73. Execution Trace
for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; }
cout << "all done" << endl;
i is 0
i is 1
i is 2
all done i 3

74. Table Revisiting const int TableSize = 20; long Entry = 1;
cout << "i" << "\t\t" << "2**i" << endl;
for (int i = 0; i <= TableSize; ++i) { cout << i << "\t\t" << Entry << endl; Entry *= 2; }

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

76. 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 Side = 0.4;
RectangleShape S(W, x, y, Blue, Side, Side);
S.Draw(); }

77. Sample Display

78. 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(); }
The scope of i includes the inner loop. The scope of j is just the inner loop.

79. Sample Display

80. 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;

81. For Into While Observation The for statement is equivalent to {
ForInit;
while (ForExpression) {
Action;
PostExpression; }

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

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

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

85. 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

86. The Do-While Statement
Syntax
do Action
while (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
Action
true
Expression
false

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