1. COMS 261 Computer Science I
Title: C++ Fundamentals
Date: September 13, 2004
Lecture Number: 10

2. Announcements
Read 4.1 – 4.6
Homework

3. Review Standard data types Names Precedence
Strings (not part of C++, but are common)
Real (float)
Names
Precedence

4. Outline
Assignment Statement
const
Non-fundamental Types
string

5. Memory Depiction
1001
1002
1003
1004
1005
1006
1007
1008
1009
100a
100b .
ffff

6. Memory Depiction float y = 12.5; float occupies 4 bytes
int temperature = 32;
char letter = 'c';
1001
1002 y
1003
12.5
1004
1005
1006
1007
Temperature 32
1008
1009
Letter c
100a
100b .
ffff

7. Assignment Statement Basic form Action object = expression ;
celsius = (fahrenheit - 32) * 5 / 9;
y = m * x + b;
Action
Expression is evaluated
Expression value stored in object

8. Definition
int NewStudents = 6;

9. Definition
int newStudents = 6;
int oldStudents = 21;

10. Definition int newStudents = 6; int oldStudents = 21;
int totalStudents;

11. Assignment Statement int newStudents = 6; int oldStudents = 21;
int totalStudents;
totalStudents = newStudents + oldStudents;

12. Assignment Statement int newStudents = 6; int oldStudents = 21;
int totalStudents;
totalStudents = newStudents + oldStudents;

13. Assignment Statement int newStudents = 6; int oldStudents = 21;
int totalStudents;
totalStudents = newStudents + oldStudents;
oldStudents = totalStudents;

14. Assignment Statement int newStudents = 6; int oldStudents = 21;
int totalStudents;
totalStudents = newStudents + oldStudents;
oldStudents = totalStudents;

15. Consider
int value1 = 10;

16. Consider
int value1 = 10;
int value2 = 20;

17. Consider
int value1 = 10;
int value2 = 20;
int hold = value1;

18. Consider int value1 = 10; int value2 = 20; int hold = value1;
value1 = value2;

19. Consider int value1 = 10; int value2 = 20; int hold = value1;
value1 = value2;

20. Consider int value1 = 10; int value2 = 20; int hold = value1;
value1 = value2;
value2 = hold;

21. Consider
int value1 = 10;
int value2 = 20;
int hold = value1;
value1 = value2;
value2 = hold;
We swapped the values of objects Value1 and Value2 using Hold as temporary holder for Value1’s starting value!

22. Incrementing int i = 1; i = i + 1;
Assign the value of expression i + 1 to i
Evaluates to 2

23. Const Definitions
Modifier const indicates that an object cannot be changed
Object is read-only
Useful when defining objects representing physical and mathematical constants
const float Pi = ;

24. Const Definitions
Value has a name that can be used throughout the program
const int SampleSize = 100;
Makes changing the constant easy
Only need to change the definition and recompile

25. Assignment Conversions
Floating-point expression assigned to an integer object is truncated
Integer expression assigned to a floating-point object is converted to a floating-point value

26. Assignment Conversions
float y = 2.7;
int i = 15;
int j = 10;
i = y; // i is now 2
cout << i << endl;
y = j; // y is now 10.0
cout << y << endl;

27. Nonfundamental Types
Nonfundamental as they are additions to the language
C++ permits definition of new types and classes
A class is a special kind of type
Class objects typically have
Data members that represent attributes and values
Member functions for object inspection and manipulation
Members are accessed using the selection operator j = s.size();
selection operator

28. Nonfundamental Types
Libraries often provide special-purpose types and classes
Programmers can also define their own types and classes
Examples
Standard Template Library (STL) provides class string
Class string
Used to represent a sequence of characters as a single object

29. Class string Some definitions string name = "Joanne";
string decimalPoint = ".";
string empty = "";
string copy = name;
string question = '?'; // illegal

30. Nonfundamental Types
To access a library use a preprocessor directive to add its definitions to your program file
#include <string>

31. Nonfundamental Types The using statement makes syntax less clumsy
Without it
std::string s = "Sharp";
std::string t = "Spiffy";
With it
using namespace std; //std contains string
string s = "Sharp";
string t = "Spiffy";

32. Class string Some string member functions
size() determines number of characters in the string
string Saying = "Rambling with Gambling";
cout << Saying.size() << endl; // 22
substr() determines a substring (Note first position has index 0)
string Word = Saying.substr(9, 4); // with

33. Class string find() computes the position of a subsequence
int j = Saying.find("it"); // 10
int k = Saying.find("its"); // ?

34. Class string Auxiliary functions and operators
getline() extracts the next input line
string Response;
cout << "Enter text: ";
getline(cin, Response, '\n');
cout << "Response is \"" << Response
<< "\"” << endl;
Example run
Enter text: Want what you do
Response is "Want what you do"

35. Class string Auxiliary operators + string concatenation
string Part1 = "Me";
string Part2 = " and ";
string Part3 = "You";
string All = Part1 + Part2 + Part3;
+= compound concatenation assignment
string ThePlace = "Brooklyn";
ThePlace += ", NY";

36. #include <iostream>
using namespace std;
int main() {
cout << "Enter the date in American format: "
<< "(e.g., January 1, 2001) : ";
string Date;
getline(cin, Date, '\n');
int i = Date.find(" ");
string Month = Date.substr(0, i);
int k = Date.find(",");
string Day = Date.substr(i + 1, k - i - 1);
string Year = Date.substr(k + 2, Date.size() - 1);
string NewDate = Day + " " + Month + " " + Year;
cout << "Original date: " << Date << endl;
cout << "Converted date: " << NewDate << endl;
return 0; }

37. 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

38. Boolean Algebra Truth tables Example
Lists all combinations of operand values and the result of the operation for each combination
Example
P Q P and Q
False False False
False True False
True False False
True True True

39. Boolean Algebra Or truth table P Q P or Q False False False
False True True
True False True
True True True

40. Boolean Algebra
Not truth table
P not P
False True
True False

41. Boolean Algebra
Can create complex logical expressions by combining simple logical expressions
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
False True False True
True False False True
True True True False

42. 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

43. 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));

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

45. 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);

46. 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

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

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

49. 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

50. 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

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

52. 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;

53. Semantics

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

55. 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"; }
Expression
Action1
Action2
true
false

56. 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;

57. Finding the Max

58. 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

59. 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;

60. 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; }

61. 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; }