bim211 – visual programming variables 1. contents variables 2
TRANSCRIPT
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BIM211 – Visual Programming
Variables
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Contents
• Variables
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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.
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Visual C# Data Types
• In Visual C#, there are two categories of data types:– Value types– Reference types
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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
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Floating Value Types
Type Approx. Range Precision Sizefloat ±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
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* Use decimal for currencies.
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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.
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Reference Types
Type 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.
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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
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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
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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);
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Some Common Methods of Convert Class
Method Converts toToBoolean boolToByte byteToSByte sbyteToChar charToDateTime DateTimeToInt16 shortToInt32 intToInt64 long
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Some Common Methods of Convert Class
Method Converts toToDecimal decimalToDouble doubleToSingle floatToString stringToUInt16 ushortToUInt32 uintToUInt64 ulong
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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.
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Where to put variables?
• Put variables in the class definition above the methods
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Arrays
• string[] strMyArray;• strMyArray = new string[10];
• Accessing elements:• strMyArray[0] = "BIM211";• strMyArray[1] = "Visual Programming";
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Multidimensional Arrays
• int[,] intMeasurements;• intMeasurements = new int[3, 2];
• Accessing elements:• intMeasurements[0, 0] = 1;• intMeasurements[2, 1] = 6;
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Constants
• You can define constant variables whose value can not be changed during the program execution by keyword const:
• const double PI = 3.14159;
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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)
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FormClosing Event
if (m_blnPromptOnExit){ if (MessageBox.Show(“Close the Picture Viewer
program?”, “Confirm Exit”, MessageBoxButtons.YesNo, MessageBoxIcon.Question)
== DialogResult.No) { e.Cancel = true; }}
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Arithmetic Operations
• Arithmetic operations are same as C but you may prefer to read chapter 12 of the textbook.
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String Operations
• Length• SubString()• IndexOf()• Trim(), TrimStart(), TrimEnd(), Remove()• Replace()
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Date/Time Operations
• DateTime dateMyBirthday = new DateTime(2008,7,22);
• AddDays(), AddHours(), etc.• ToLongDateString()• ToShortDateString()• ToLongTimeString()• ToShortTimeString()
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Date/Time Operations
• DateTime.Today• DateTime.Now
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