1. CS0004: Introduction to Programming Variables – Strings

2. 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 value

3. 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()

4. String  A string 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, variableName2 As String

5. String Example  New Topics:  String declaration  String literal  String variable

6. 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 it

7. 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)

8. 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 operators

9. Typecasting and Concatenation Example  New Topics:  Option Strict  Option Explicit  Concatenation between string  Concatenation between a string and a number  Explicit typecasting to double  Explicit typecasting to string

10. 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

11. String Properties and Methods Example  New Topics:  Length  ToUpper  ToLower  Trim  Substring  IndexOf

12. 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 webpage

13. 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