BİL528 – Bilgisayar Programlama II

Variables

1

Contents

• Variables

2

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.

3

Visual C# Data Types

• In Visual C#, there are two categories of data types:– Value types– Reference types

4

Integral Value TypesType Approx. Range Sizebyte 0 to 255 1 bytesbyte –128 to 127 1 bytechar U+0000 to U+FFFF 2 bytesshort –32768 to 32767 2 bytesushort 0 to 65535 2 bytesint –2,147,483,648 to 2,147,483,647 4 bytesuint 0 to 4,294,967,295 4 byteslong –9,223,372,036,854,775,808 to

9,223,372,036,854,775,8078 bytes

ulong 0 to 18,446,744,073,709,551,615 8 bytes5

Floating Value Types

Type Approx. Range Precision Sizefloat ±1.5 × 10−45 to

±3.4 × 10387 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

6

* Use decimal for currencies.

Other Value Types

Type Explanationbool Stores Boolean values, true and falseenum Enumeration. Example:

enum Days {Mon, Tue, Wed, Thu, Fri, Sat, Sun};

struct Lightweight version of class.

7

Reference TypesType Explanationstring Unicode character arraysobject Everything in C# is inherited from object class

directly or indirectlyclass Blueprint of objectsdelegate Method signature (like function pointers in C)interface An interface contains only the signatures

of methods, properties, events or indexers.

8

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

9

Safe Conversions

Type Can Be Safely Converted Tobyte short, int, long, float, double, decimalshort int, long, float, double, decimalint long, float, double, decimallong float, double, decimalfloat doubledouble decimal

10

Explicitly Converting Data

• Simplest way is using C syntax:– double d = 2.3;– int i = (int) d;

• You can also use Convert class:– double d = 2.3;– int i = Convert.ToInt32(d);

11

Some Common Methods of Convert Class

Method Converts toToBoolean boolToByte byteToSByte sbyteToChar charToDateTime DateTimeToInt16 shortToInt32 intToInt64 long

12

Some Common Methods of Convert Class

Method Converts toToDecimal decimalToDouble doubleToSingle floatToString stringToUInt16 ushortToUInt32 uintToUInt64 ulong

13

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.

14

Where to put variables?

• Put variables in the class definition above the methods

15

Arrays

• string[] strMyArray;• strMyArray = new string[10];

• Accessing elements:• strMyArray[0] = "BIM211";• strMyArray[1] = "Visual Programming";

16

Multidimensional Arrays

• int[,] intMeasurements;• intMeasurements = new int[3, 2];

• Accessing elements:• intMeasurements[0, 0] = 1;• intMeasurements[2, 1] = 6;

17

Constants

• You can define constant variables whose value can not be changed during the program execution by keyword const:

• const double PI = 3.14159;

18

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)

19

FormClosing Event

if (m_blnPromptOnExit){ if (MessageBox.Show(“Close the Picture Viewer

program?”, “Confirm Exit”, MessageBoxButtons.YesNo, MessageBoxIcon.Question)

== DialogResult.No) { e.Cancel = true; }}

20

Arithmetic Operations

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

21

String Operations

• Length• SubString()• IndexOf()• Trim(), TrimStart(), TrimEnd(), Remove()• Replace()

22

Date/Time Operations

• DateTime dateMyBirthday = new DateTime(2008,7,22);

• AddDays(), AddHours(), etc.• ToLongDateString()• ToShortDateString()• ToLongTimeString()• ToShortTimeString()

23

Date/Time Operations

• DateTime.Today• DateTime.Now

24