CS0004: Introduction to Programming

1. CS0004: Introduction to Programming Variables – Numbers

2. Review • The basic form of setting a property of a control: controlName.property = setting txtBox.ForeColor = Color.Red Private Sub btnButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnButton.Click ‘Code goes here End Sub • There’s only two parts you need to worry about: • btnButton_Click is the name of the event procedure • btnButton.Click tells the procedure to listen for the click event on the button btnButton. • To make an event procedure you can: • Double click on the control (creates the default event procedure for the control) • Click on the control then click the “Events” button at the top of the Properties Window

3. Numeric Literals and Arithmetic Operations • Data appearing as numbers are called numeric literals. • 3 • 4 • 9.9 • With these we can perform various arithmetic operations with arithmetic operators: • Addition + • Subtraction - • Multiplication * • Division / • Exponentiation ^ • Grouping Symbols () • The arithmetic operators follow normal order of operations

4. Arithmetic Operations Example • See Example on Course Webpage • New Things: • Numeric Literals • Arithmetic Operations • List Box • lstExample.Items • Accesses the list boxes items • lstExample.Items.Clear() • Removes all items from the list box • lstExample.Items.Add(parameter) • Adds the supplied parameter to the list as a list item • Add and Clear are known as methods • A method is a process that performs a task for a particular object. • What is in the “()” in the Add method is called a parameter. • A parameter is information passed to the method to be processed • Not all methods require parameters (Clear, for example, doesn’t)

5. Variables • In math problems quantities are referred to by name. • For example, if we wanted to see how far a car traveled if the car was going 50 miles per hour for 14 hours? • How would we solve this? • Take the speed (50 miles per hour) • Multiply it by the time elapsed (14 hours) • To get the distance traveled distance = speed x time elapsed • This can be solved by a computer program.

6. Variables Example • See Example on Course Webpage • New Things: • Variables – speed, timeElapsed, and distance are variables • Variables can be thought of boxes where we store values. • You access variables by using their names. • Camel Casing • When you want something to be named a series of words DO NOT put spaced between the words, use camel casing instead. • Camel casing is capitalizing the next work instead of using a space. • timeElapsed • Assignment Statement • An assignment statement puts a value into a variable. Uses the assignment operator (=)’ • speed = 50 • Declaration Statement • It is good practice to declare a variable before using it. • This allows the program to free up space for the variable in memory. • Dim speed As Double

7. Declaration Statement • The form of a declaration statement in VB is: Dim variableName As type • variableName is whatever you decide to name the variable • Naming rules: • Variable names must start with an alphabetic character or an underscore (_) • After the first character they can have any alphabetic, numeric, or underscore character • Keywords cannot be used as variable names • type is what type of information the variable can hold. • Two numeric types: • Double – can hold positive or negative floating-point (decimal) values • Example: 3.4, 90.222, 4.97635 • Integer – can hold positive or negative whole numbers • Examples: 1, 3, 573

8. Initialization • If a variable is assigned a value right after it is declared, you can combine the two into one statement: Dim speed As Double speed = 50 Becomes… Dim speed As Double = 50 • This is called an initialization statement. • Again, this makes the variable speed have to value of 50

9. Some Built-In Functions • You can do some more complex math operations such as square root and round. • To do this, we use some of VBs built-in functions. • Functions are methods that return a value. • Returning a value means doing some computation and supplying some value where the function is used (or called). • Square Root and Round are functions of the Math object. So, to access them, you must do: • Math.Sqrt(parameter) • Math.Sqrt(9) is 2 • Math.Round(paramer) • Math.Round(3.6) is 4 • Sometimes you want to convert a double into an integer by cutting off the decimal portion • Int(parameter) • Int(3.6) is 3

10. Notes • You can declare multiple variables in one line. Dim a As Double Dim b As Double Becomes… Dim a, b As Double Or Dim a As Double = 2 Dim b As Double = 5 Becomes… Dim a As Double = 2, Dim b As Double = 5 • In addition to the mathematical operators mentioned before, there are two specific for integers: • Integer Division (\) • 14 \ 3 is 4 • Modulus – (Mod) • 14 Mod 3 is 2

11. Notes • You can mix numeric literals, variables, and arithmetic operators can be mixed • answer = x + (4 - y) * 6 • Often times you want to perform an operation to a variable then store it back into the original variable • Example: x = x + 1 • You can simplify this by using the += operator • Example: x += 1 • There are two special numeric values in VB • NaN – Not a Number • Example: Math.Sqrt(-1) • Infinity • Example: 1/0

12. Numbers Notes Example • See Example on Course Webpage • New Things: • Initialization • Multiple declarations in one line • Integers • -= operator • Square Root • Round • Int • Integer Division • Modulus

13. Errors • Two Types Introduced Before: • Syntax Error – Gramatical Errors to the VB language • Misspellings, omissions, incorrect punctuations, etc. • Logical Error – When the program does not perform the way it is intended • Typing a = b + c when you mean a = b – c, for example • Another Type: • Runtime Error – Some error the compiler could not check before making the executable. • Often due to influence outside of the program • Error List Window