CS4 Lecture 4: Intro to Programming with Visual Basic - Variables & Arithmetic, Study notes of Computer Science

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CS 0004 – Introduc/on to

Programming

Using Visual Basic Summer 2009 University of Pi@sburgh Lecture 4

Chapter 3.1‐3.

Variables

Numbers and Strings

Arithme/c Opera/ons

Vocabulary words

• Numeric expression
  • A combina/on of literals, variables, and arithme/c opera/ons that can be evaluated to yield a number
• Increment
  • Add to a value
• Decrement
  • Subtract from a value
    • Syntax error
      • Gramma/cal error such as misspellings, omissions, or incorrect punctua/on
    • Excep/ons
      • Also called run‐/me errors, happen while a program is running
    • Keywords
      • Reserved words

Variables vs. Literals

• Variables are symbols that hold a value
  • In math, you use
    • x
    • y
  • In programming you can use
    • total
    • numCupcakes
    • name
• Literals are values
  • 5
  • “When does class start?”

Declaring Variables

• Every variable should be declared before it is

used

• Declare variables at the top of a method
• Declara/on statement
• Dim variableName As VariableType
• Such as:
• Dim numCupcakes As Integer
• Dim address As String
• Dim totalBill As Double

Variable Types

• Double
  • Numbers that may have decimal component, between about nega/ve and posi/ve 1.8* 308
• Integer
  • Whole numbers, between about nega/ve and posi/ve 2 billion
• String
  • Contains zero or more characters
  • “210 S. Bouquet Street” is a string

Control Proper/es as Variables

• Proper/es of controls are also variables
• We can change them, even as the program is

running

• Remember changing the text of a bu@on?
• Remember turning the text different colors?

Math!

Let’s try some math

• Open Visual Studio 2008
• Start a new project
• While that’s loading, let’s talk about…

Methods

• Process that performs a task for a par/cular

object

• Examples of methods:
  • lstBox.Items.Clear()
    • Clear() is a method that acts on the Items property of lstBox
  • lstBox.Items.Add(“Alpha”)
    • Add() is a method that acts on the Items property of lstBox

Built‐in Math Func/ons

• Math.Sqrt
  • Math.Sqrt(9) = 3
  • Math.Sqrt(2) = 1.414214…
• Int
  • Nearest whole number less than the one given
  • Int(3.8) = 3
  • Int(‐5.3) = ‐
• Math.Round
  • Rounds to nearest whole number
  • In case of halfway between two numbers, round to the even number
  • Math.Round(2.5) = 2
  • Math.Round(3.5) = 4

Let’s try some math func/ons

• Inside the event handler for btnCompute.Click
  • lstResults.Clear()
  • lstResults.Add(Math.Sqrt(25))
  • lstResults.Add(Int(5.2)*Math.Round(4.5) )
  • Others?

Concatena/ng Strings

• Let’s say you have 2 strings that you want to

join…

• Dim firstName, lastName, fullName As String
• firstName = “Ada”
• lastName = “Lovelace”
• Join them together with &
• fullName = firstName & lastName
• But this gives “AdaLovelace”
• fullName = firstName & “ ” & lastName
• Now fullName = “Ada Lovelace”

String Length ‐ Property

• String property: Length
  • Dim str As String
    • Remember to declare variables before using
  • str = “Good Morning”
    • str.Length is 12
  • Str = “”
    • Str.Length is 0