1. BİL528 – Bilgisayar Programlama II
Variables

2. Contents
Variables

3. Variables
In your programs, you must determine the type of your data (int, string, etc.)
In object oriented programming languages, you must also determine the level of visibility of your data (public, private, etc).
This visibility is known as scope.

4. Visual C# Data Types
In Visual C#, there are two categories of data types:
Value types
Reference types

5. Integral Value Types Type Approx. Range Size byte 0 to 255 1 byte
sbyte
–128 to 127
char
U+0000 to U+FFFF
2 bytes
short
–32768 to 32767
ushort
0 to 65535
int
–2,147,483,648 to 2,147,483,647
4 bytes
uint
0 to 4,294,967,295
long
–9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
8 bytes
ulong
0 to 18,446,744,073,709,551,615

6. Floating Value Types Type Approx. Range Precision Size float
±1.5 × 10−45 to ±3.4 × 1038
7 digits
32 bits
double
±5.0 × 10−324 to ±1.7 × 10308
15-16 digits
64 bits
decimal
±1.0 × 10−28 to ±7.9 × 1028
28-29 digits
128 bits
* Use decimal for currencies.

7. Other Value Types Type Explanation bool
Stores Boolean values, true and false
enum
Enumeration. Example:
enum Days {Mon, Tue, Wed, Thu, Fri, Sat, Sun};
struct
Lightweight version of class.

8. Reference Types Type Explanation string Unicode character arrays
object
Everything in C# is inherited from object class directly or indirectly
class
Blueprint of objects
delegate
Method signature (like function pointers in C)
interface
An interface contains only the signatures of methods, properties, events or indexers.

9. Type Casting
There are two types of type casting: Implicit and Explicit
Implicit conversions are done automatically by the compiler
Widening cast
No data loss
Example: conversion from float to double
Explicit conversions require programmers approval
Narrowing cast
Data may be lost
Example: conversion from double to float

10. Safe Conversions Type Can Be Safely Converted To byte
short, int, long, float, double, decimal
short
int, long, float, double, decimal
int
long, float, double, decimal
long
float, double, decimal
float
double
decimal

11. Explicitly Converting Data
Simplest way is using C syntax:
double d = 2.3;
int i = (int) d;
You can also use Convert class:
int i = Convert.ToInt32(d);

12. Some Common Methods of Convert Class
Converts to
ToBoolean
bool
ToByte
byte
ToSByte
sbyte
ToChar
char
ToDateTime
DateTime
ToInt16
short
ToInt32
int
ToInt64
long

13. Some Common Methods of Convert Class
Converts to
ToDecimal
decimal
ToDouble
double
ToSingle
float
ToString
string
ToUInt16
ushort
ToUInt32
uint
ToUInt64
ulong

14. Declaring Variables datatype variable_name = initial_value;
int a;
string str = "BIM211";
double m = 10, n = 20;
long k, l = 100;
Visual C# is a strongly typed language; therefore, you must always declare the data type of a variable.
In addition, Visual C# requires that all variables be initialized before they’re used.

15. Where to put variables?
Put variables in the class definition above the methods

16. Arrays string[] strMyArray; strMyArray = new string[10];
Accessing elements:
strMyArray[0] = "BIM211";
strMyArray[1] = "Visual Programming";

17. Multidimensional Arrays
int[,] intMeasurements;
intMeasurements = new int[3, 2];
Accessing elements:
intMeasurements[0, 0] = 1;
intMeasurements[2, 1] = 6;

18. Constants
You can define constant variables whose value can not be changed during the program execution by keyword const:
const double PI = ;

19. Exercise
Create a boolean variable to store whether a confirmation box appears or not
Change its value when “Confirm on exit” menu item is clicked
Handle the FormClosing event and write the following code:
(see next slide)

20. FormClosing Event
if (m_blnPromptOnExit) { if (MessageBox.Show(“Close the Picture Viewer program?”, “Confirm Exit”, MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.No) e.Cancel = true; }

21. Arithmetic Operations
Arithmetic operations are same as C but you may prefer to read chapter 12 of the textbook.

22. String Operations Length SubString() IndexOf()
Trim(), TrimStart(), TrimEnd(), Remove()
Replace()

23. Date/Time Operations
DateTime dateMyBirthday = new DateTime(2008,7,22);
AddDays(), AddHours(), etc.
ToLongDateString()
ToShortDateString()
ToLongTimeString()
ToShortTimeString()

24. Date/Time Operations
DateTime.Today
DateTime.Now