1. COMS 261 Computer Science I
Title: C++ Fundamentals
Date: September 14, 2005
Lecture Number: 8

2. Announcements Homework Read Sections 2.6 – 2.11 and 3.1 – 3.6
Due Thursday, September 15, 2005
2.7, 2.15, 2.16, 2.19, 2.20
Read Sections 2.6 – 2.11 and 3.1 – 3.6
Read/scan Lab 2 before tomorrow
Know what you did in Lab 1
Goal is to learn, not to just get it done!!

3. Review
Standard data types
Integer
Real (float)
Character

4. Outline
Keywords
Identifiers
Operator Precedence

5. Names Used to denote program values or components
A valid name is a sequence of
Letters (upper and lowercase)
Digits
A name cannot start with a digit
Underscores
A name should not normally start with an underscore

6. Names Names are case sensitive There are two kinds of names
MyObject is a different name than MYOBJECT
There are two kinds of names
Keywords
Identifiers

7. Keywords Keywords are words reserved as part of the language
int, return, float, double, this
Colored blue in CodeWarrior
They cannot be used by the programmer to name (label) things in the program
They consist of lowercase letters only
They have special meaning to the compiler

8. Identifiers Identifiers should be
Short enough to be reasonable to type (single word is norm)
Standard abbreviations are fine (but only standard abbreviations)
Long enough to be understandable
When using multiple word identifiers capitalize the first letter of each word
Examples
min, temperature, cameraAngle, currentNumPoints

9. Definitions All objects used in a program must be defined
An object definition includes
Type
Name
General definition form
Our convention is one definition per statement!

10. Examples char Response; int MinElement; float Score;
float Temperature;
int i;
int n;
char c;
float x;
Objects are uninitialized with this definition form
(Value of a object is whatever is in its assigned memory location)

11. Arithmetic Operators Common Addition + Subtraction - Multiplication *
Division /
Mod %
Write m*x + b not mx + b

12. Arithmetic Operators Note No exponentiation operator
Single division operator
Integer and float
Operators are overloaded to work with more than one type of object

13. Integer Division Integer division produces an integer result Examples
Truncates
Throws away the fractional part of the result
Examples
3 / 2 evaluates to 1
4 / 6 evaluates to 0
10 / 3 evaluates to 3

14. Mod Produces the remainder of the division Examples
5 % 2 evaluates to 1
2 goes into 5, 2 times with a remainder of 1
12 % 4 evaluates to 0
4 goes into 12, 3 times with a remainder of 0
4 % 5 evaluates to 4
5 goes into 4, 0 times with a remainder of 4

15. Operators and Precedence
Consider mx + b
which of the following is it equivalent to
(m * x) + b
m * (x + b)
Operator precedence tells how to evaluate expressions

16. Operators and Precedence
Standard precedence order
() Evaluate first, if nested innermost done first
* / % Evaluate second. If there are several, then evaluate from left-to-right
+ - Evaluate third. If there are several, then evaluate from left-to-right

17. Operator Precedence Examples 20 - 4 / 5 * 2 + 3 * 5 % 4 (4 / 5)
/ 5 * * 5 % 4
(4 / 5)
((4 / 5) * 2)
((4 / 5) * 2) (3 * 5)
((4 / 5) * 2) ((3 * 5) % 4)
(20 -((4 / 5) * 2)) ((3 * 5) % 4)
(20 -((4 / 5) * 2)) + ((3 * 5) % 4)

18. Defining and Initializing
When an object is defined using the basic form, the memory allotted to it contains random information
Better idea to specify its desired value at the same time
Exception is when the next statement is an extraction for the object
Remember our convention of one definition per statement!

19. Examples int FahrenheitFreezing = 32; char FinalGrade = 'A';
cout << "Slope of line: ";
float m;
cin >> m;
cout << "Intercept: ";
float b;
cin >> b;
cout << "X value of interest: ";
float x;
cin >> x;
float y = (m * x) + b;

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

21. 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

22. 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

23. Definition
int NewStudents = 6;

24. Definition
int NewStudents = 6;
int OldStudents = 21;

25. Definition int NewStudents = 6; int OldStudents = 21;
int TotalStudents;

26. Assignment Statement int NewStudents = 6; int OldStudents = 21;
int TotalStudents;
TotalStudents = NewStudents + OldStudents;

27. Assignment Statement int NewStudents = 6; int OldStudents = 21;
int TotalStudents;
TotalStudents = NewStudents + OldStudents;

28. Assignment Statement int NewStudents = 6; int OldStudents = 21;
int TotalStudents;
TotalStudents = NewStudents + OldStudents;
OldStudents = TotalStudents;

29. Assignment Statement int NewStudents = 6; int OldStudents = 21;
int TotalStudents;
TotalStudents = NewStudents + OldStudents;
OldStudents = TotalStudents;

30. Consider
int Value1 = 10;

31. Consider
int Value1 = 10;
int Value2 = 20;

32. Consider
int Value1 = 10;
int Value2 = 20;
int Hold = Value1;

33. Consider int Value1 = 10; int Value2 = 20; int Hold = Value1;
Value1 = Value2;

34. Consider int Value1 = 10; int Value2 = 20; int Hold = Value1;
Value1 = Value2;

35. Consider int Value1 = 10; int Value2 = 20; int Hold = Value1;
Value1 = Value2;
Value2 = Hold;

36. 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!

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

38. 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 = ;

39. 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

40. 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

41. 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;