CS0004: Introduction to Programming

CS0004: Introduction to Programming Variables – Strings

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

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()

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, variableName2As String

String Example • New Topics: • String declaration • String literal • String variable

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

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)

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 winnerStringAs String = “And the winner is contestant #” Dim winnerNumberAs Integer = 2 Dim winner As String winner = winnerString& winnerNumber • There is a &= operator like with the arithmetic operators

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

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

String Properties and Methods Example • New Topics: • Length • ToUpper • ToLower • Trim • Substring • IndexOf

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

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

CS0004: Introduction to Programming