CS0004: Introduction to Programming - PowerPoint Presentation

Slide1

CS0004: Introduction to Programming

Variables –

StringsSlide2

Review

Data appearing as numbers are

called…

Numeric

literals.

Arithmetic Operators

Addition +

Subtraction -

Multiplication *

Division /

Exponentiation ^

Grouping Symbols

()

A method is…

A process that performs a task for a particular object

Variables are…

Named memory locations that can hold values

A method is

…

A

process that performs a task for a particular

object

A function is…

A method that returns a

valueSlide3

Review

A parameter is…

Information passed to a method or function to be

processed

Declaration Statement General Form:

Dim

variableName

As Type

An assignment statement …

Puts a value into a variable. Uses the assignment operator (=)

Some integer arithmetic operators

Integer Division (\)

Modulus (Mod)

More complex math operations

Math.Sqrt

()

Math.Round

()

Int

()Slide4

String

A

s

tring literal

is a sequence of characters that is treated as a single item

Examples:

“Banana”

“It can have spaces”

“It can have special characters!!^$&(”

“”

This is the

empty string

a string with no characters

String literals are surrounded in double quotes (

“ ”

)

A

string variable

is a variable that holds a string (is of the string data type)

To declare a string variable:

Dim

variableName

As String

You can also initialized a string variable

Dim

variableName

As

String = “banana”

And also declare more than one on a single line

Dim

variableName1, variableName

2

As StringSlide5

String Example

New Topics:

String

d

eclaration

String literal

String variableSlide6

Text Boxes

The content of a text box is always a string, so you can do things such as:

Dim answer As String

answer =

txtAnswer.Text

Or…

txtAnswer.Text

= answer

However by default you can do things like:

Dim number As Integer

number =

txtAnswer.Text

This is known as

implicit typecasting

: THIS IS BAD PROGRAMMING PRACTICE!

Typecasting

– converting from one type to another

To prevent the urge to do this you should put

Option Strict On

at the top of the code to your form

This will make the compiler not allow implicit typecasting

Also, you should put the line

Option

Explicit On

at the top

This will make the compiler not allow you to use a variable before you declare itSlide7

Explicit Typecasting

So what if we want to take user input data that is a number?

Answer: Explicit Typecasting

You can use a pre-defined function to explicitly typecast a string to a double or integer or vice versa:

CDbl

(parameter)

– typecasts to double

CInt

(parameter)

– typecasts to integer

CStr

(parameter)

– typecasts to string

If you do some calculation with a number, and you want to put the result in a text box, you should typecast the number into string first

txtBox.Text

=

CStr

(result)Slide8

Concatenation

You can combine multiple strings into one string using the

concatenation operator

(&)

Dim groceryList1 As String = “bread, milk, ”

Dim groceryList2 As String = “eggs, apples”

Dim

fullGroceryList

As String

fullGroceryList

= groceryList1 & groceryList2

You can also concatenate strings with number data types

Dim

winnerString

As String =

“And the winner is contestant #”

Dim

winnerNumber

As

Integer

= 2

Dim

winner

As String

winner

=

winnerString

&

winnerNumber

There is a

&=

operator like with the arithmetic operatorsSlide9

Typecasting and Concatenation Example

New Topics:

Option Strict

Option Explicit

Concatenation between

s

tring

Concatenation between a string and a number

Explicit typecasting to double

Explicit typecasting to stringSlide10

String Properties and Methods

You can get certain information about a string and perform some actions on it with some of VBs predefined properties and methods (Assume we have a string

str

)

str.Length

– returns how many characters are in the string

str.ToUpper

– returns all the characters in the string in upper-case

str.ToLower

– returns all the characters in the string in lower-case

str.Trim

– returns a string with all the spaces at the beginning and end removed

str.Substring

(param1, param2)

– returns a portion of the string starting at the character at

param1

to the character at

param2

Note: The numbering of the characters start at 0, so the first character is 0, the second is 1, and so on

str.IndexOf

(param1)

– returns the position of the first

occurance

of the substring

param1

, -1 if

param1

is not a substring of

str

Slide11

String Properties and Methods Example

New Topics:

Length

ToUpper

ToLower

Trim

Substring

IndexOfSlide12

Documentation

Comments

– are lines of code that are ignored by the compiler

Often used to write notes in the code to explain what is does

Comments in VB start with

‘

‘Here I am just declaring a variable

Dim

variableName

As Integer

It is good programming practice to have comments in your code to give an overview of what a section does

Good Examples

‘Here I compute the distance traveled

‘Below I take the user’s input

‘Now I output the answer to the results text box

Bad Examples

‘This code works but I don’t know why

‘More lines of code

‘Taken from the course webpageSlide13

File Comment Block

At the top of all of your project I want you to include the following information

Author’s Name

Course

Date Due

Brief Description

‘ Author: Eric Heim

‘ Course: CS0004

‘ Date Due: 2/2/2011

‘ Description: This code computes the distance

‘ traveled by a car by taking in the

‘ speed it was going and how long it

‘ was driving