1. Documentation Need to have documentation in all programs
Documentation header
Regular comments inside programs
Follow department standard
Copy-and-paste shell command in Putty
Highlight the part to copy
Right-click to paste

2. Review Q. What does #include do? Q. What is namespace std?
Q. How many main( ) function(s)?
Q. What does a preprocessor do?
cout
cout<<“Hello “<< “World!”<<endl;
“\n” and endl
Refer to example in PPT2

3. Variable Named memory location Used to hold data Name Type Capacity
Different type holds different kinds of data
Capacity
How large is this location?
Determined by type
Duration
Gets recycled after lifetime is over
pp67-68

4. To define a variable Specify type and name
int num; // reserve a location of four bytes in RAM
// used for storing an integer
// reference the location using name num
Define several variables of same type in an instruction
int rate, hour, pay; //reserve three locations with four bytes each
pp67

5. Rules for choosing variable names
Use numbers, letters, underscore
Cannot start with number
Cannot be keywords
Make it meaningful
C++ is case sensitive!
Hour and hour are two different variables!
pp68

6. Valid and Invalid variable names
IDENTIFIER
VALID?
REASON IF INVALID
totalSales
total_Sales
total.Sales
4thQtrSales
totalSale$

7. Valid and Invalid variable names
IDENTIFIER
VALID?
REASON IF INVALID
totalSales
Yes
total_Sales
total.Sales No
Cannot contain .
4thQtrSales
Cannot begin with digit
totalSale$
Cannot contain $

8. Variable Type: Integer
positive and negative whole numbers,
e.g. 5, -52,
short, int, long
represented internally in binary
16 is represented as
To define:
int number;
pp63

9. Variable Type: Floating point number
Real number (integral and fractional part)
2.5, , , 5.0
float, double, long double
Stored internally as mantissa and exponent (base 2)
16.0 is represented as mantissa 1.0 and exponent 4
pp64

10. Variable Type: Floating point number
To define:
float amount;
double hour, rate;
pp64

11. Variable Type: Boolean
Logical variable
Named for George Boole
Values: true and false
To define:
bool flag;
pp65

12. Variable Type: Character
represent individual character values
E.g. ’A’ ’a’ ’2’ ’*’ ’”’ ’ ’
stored in 1 byte of memory
special characters: escape sequences
’\n’ ’\b’ ’\r’ ’\t’ ‘\’’
To define:
char letter;
pp65

13. string type A sequence of characters
Can contain zero or more character
“” empty string
“A” string with one char
“Hello” string with five characters
pp66

14. string type
Be careful with single and double quotes (“ versus ")when using word processor
Not a primitive type (size varies)
A string can have arbitrary number of characters
pp66

15. To define a string Same syntax string course_name;
//reserve 2 or 4 bytes to store the //address of the string
//store the string dynamically in //another place
string course_name;
pp66

16. In summary For whole numbers For floating point numbers
short (2 bytes)
int (4 bytes)
long (4 or 8 bytes)
For floating point numbers
float (4 bytes)
double (8 bytes)
For single character
char (1 byte)
For Boolean (true/false) values
bool (1 bit)
For string
string (varies)

17. More examples float x, y; int num1, num2; float salary;
string flower_name;

18. Assignment operator = Two-step action
Evaluate the value of right hand side
Assign the value to left hand side
int num;
num = 5;
num = num + 1;
num = num * 2;
num = num * num;
pp71

19. Left hand side must be a variable
12 = item;
// ERROR! Left hand side does not reference a location
a + 5 = a;
//Same error

20. Variable initiation
Combine variable declaration and initial assignment into a single instruction
int num = 5; //declare an integer variable num
//assign 5 to num
Can also write them separately
int num;
num = 5;

21. Variable declaration without initial values
An uninitialized variable has a random value, i.e. we do not know what value is stored
int num;
char letter;
float rate;

22. Literal vs. Variable
A literal is a value that is written into a program’s code.
"hello, there" (string literal)
12 (integer literal)
‘C’ (character literal)
3.5 (floating point number literal)
Value of a literal cannot be changed.
3 is always 3.
Value of a variable can be changed.
pp63, 66

23. 20 is an integer literal

24. This is a string literal

25. This is also a string literal

26. Output a variable The current value of the variable will be printed
Don’t enclose a variable name in double quotes
int num= 5;
num = num * num;
cout << “The value of num is “ << num << endl;

27. More examples char letter = ‘c’;//declare letter, assign ‘c’ to letter
//don’t forget single quote
Q. What about the following?
char letter = c; //c is considered as a variable
//Error! may or may not compile

28. More examples
bool flag = true; // true is a keyword string name = "John"; //use double quote string name = John; // Error! John is treated as a variable name

29. Define before use

30. What is the output? int a=5, b=7, c=10; a = a + 3; b = a + c;
cout << a << “ “ << b << “ “ << c << endl;
Every object (string, variable, or manipulator) needs a separate << in a cout instruction.
//Error!
cout << a << “ “ << b << “ “ c << endl;
=>

31. Characters and strings
A character is stored as its ASCII value (Appendix B)
‘A’ 65
‘B’ 66
‘y’ 121
‘$’ 36
A string is stored as a sequence of characters
“John”
Always has the NULL character (‘\0’) at the end 74
111
104
110 \0

32. ‘A’ and “A” Q. Are they the same?
‘A’ is a single character, stored in 1 byte of memory
“A” is a string of length one, stored as 2 bytes of memory 65 65 \0

33. Summary Variable basics Literals How to declare and initialize
Various types
Assignment operator
Difference between characters and strings
Output variable values using cout
Literals

34. Review Section 2.3 Variable types and declarations