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

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.

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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