1. Lecture 2
Data Types
Richard Gesick

2. Topics Character Strings Variables and Assignments
Primitive Data Types

3. Review C# program structure Comments Identifiers White space Objects
Classes
Methods

4. Building Blocks - Comments
Comments explain the program to yourself and others
Block comments
Can span several lines
Begin with /*
End with */
Compiler ignores all text between /* and */
Line comments
Start with //
Compiler ignores text from // to end of line

5. Identifiers - symbolic names
Identifiers are used to name classes, variables, and methods
Identifier Rules:
Must start with a letter
Can contain essentially any number of letters and digits, but no spaces
Case sensitive!!
Number1 and number1 are different!
Cannot be keywords or reserved words

6. Character Strings Object in C#, defined by string class
String literal is 0 or more characters enclosed with double quotes
“The quick brown fox jumped.”
“x” “”
Can contain any valid character

7. Write and WriteLine Methods
Console.WriteLine (“Whatever you are, be a good one.”);
Output device
Monitor
Console – class
Out - objects
parameter
Method name
WriteLine method includes a “new line” character.

8. Using Write and WriteLine
Blast-off
We are go for orbit

9. string Concatenation Operator (+)
String literals cannot span lines
Combines string literals with other data types for printing
Example:
string first = "Hello";
string second = "there";
string greeting = first + “ “ + second;
Console.Out.WriteLine( greeting );
Output is:
Hello there

10. The + Operator What it does depends on the order String concatenation
addition

11. string concatenation
Bond, James Bond 007 Bond, James Bond 0034 The sum of x and y is: 2339 The sum of x and y is: 62 The sum of 23 and 39 is 62

12. Escape Sequences
To include a special character in a string, use an escape sequence

13. Escape sequences
Almost every fairy tale begins with "Once upon a time" while many mysteries start with "It was a dark and stormy night" and then you hear from the people that owe you money "the check is in the mail"

14. Multiple variables can be created in one declaration
A variable is a name for a location in memory used to hold a data value.
A variable must be declared by specifying the variable's name and the type of information that it will hold
Multiple variables can be created in one declaration
data type
variable name
int total;
int count, temp, result;

15. while a motorcycle has 2 tires
using System;
//more concatenation
namespace moreConcat {
class Program
static void Main(string[] args)
int carTires = 4;
int motorCycleTires = 2;
Console.WriteLine("A car has " + carTires + " tires"+
“\nwhile a motorcycle has " + motorCycleTires + " tires"); }
Output:
A car has 4 tires
while a motorcycle has 2 tires

16. Conventions
Names of variables should be meaningful and reflect the data they will store
This makes the logic of the program clearer
Don't skimp on characters, but avoid extremely long names
Avoid names similar to C# keywords

17. Assignment
An assignment statement changes the value of a variable
The assignment operator is the = sign
total = 55;
The expression on the right is evaluated and the result is stored in the variable on the left
The value that was in total is overwritten
You can only assign a value to a variable that is consistent with the variable's declared type

18. Assignment Operator
Syntax: target = expression; expression: operators and operands that evaluate to a single value --value is then assigned to target --target must be a variable (or constant) --value must be compatible with target's data type

19. Examples: The next statement is illegal
int numPlayers = 10; // numPlayers holds 10
numPlayers = 8; // numPlayers now holds 8
int legalAge = 18;
int voterAge = legalAge;
The next statement is illegal
int height = weight * 2; // weight is not defined
int weight = 20;

21. Declare a variable only once
Once a variable is declared, its data type cannot be changed.
These statements:
double twoCents;
double twoCents = .02;
generate a compiler error

22. Once a variable is declared, its data type cannot be changed.
These statements:
double cashInHand;
int cashInHand;
generate a compiler error

23. Constants Value cannot change during program execution Syntax:
const dataType constantIdentifier =assignedValue;
Note: assigning a value when the constant is declared is optional. But a value must be assigned before the constant is used.

24. Constants Constants are useful for three important reasons
First, they give meaning to otherwise unclear literal values
For example, MAX_LOAD means more than the literal 250
Second, they facilitate program maintenance
If a constant is used in multiple places, its value need only be updated in one place
Third, they formally establish that a value should not change, avoiding inadvertent errors by other programmers

25. Conventions
Use all capital letters for constants and separate words with an underscore:
Example:
const double TAX_RATE = .05;
Declare constants at the top of the program so their values can easily be seen
Declare as a constant any data that should not change during program execution

26. Data Types For all data, assign a name (identifier) and a data type
Data type tells compiler:
How much memory to allocate
Format in which to store data
Types of operations you will perform on data
Compiler monitors use of data
C# is a "strongly typed" language

27. Primitive Data Types 13 simple data types:
8 subsets of integers
2 subsets of floating point numbers
Character
Boolean
Decimal data type
Everything else is an object

29. Why so many types?
Difference is in amount of memory reserved for each (and hence the size of the value stored
float only has 7 significant digits
Signed numbers have both positive and negative values
Unsigned numbers are >= 0

30. Literals All numeric values without a decimal point are considered int
All numeric values with decimal point are considered double
int testGrade = 100;
long cityPopulation = L;
byte ageInYears = 19;
float salesTax = .05F;
double interestRate = 0.725;
double avogadroNumber = E23;

31. char Data Type One Unicode character (16 bits - 2 bytes)
Type Size Minimum Value Maximum Value
in Bytes
char character character
encoded as encoded as FFFF
Example declarations:
char finalGrade = ‘A’;
char newline, tab, doubleQuotes;

32. boolean Data Type Two values only:
true
false
Used for decision making or as "flag" variables
Example declarations:
bool isEmpty;
bool passed, failed = false;