A-level Computing 2009/AQA/Problem Solving, Programming, Data Representation and Practical Exercise/Fundamentals of Programming/Input and output

Comments Arithmetic operators An important part of computer code is allowing your user to input data into the program, things such as text, key presses or even a data feed from a motion sensor games controller. Once the data is in the program you want the system to output responses, these may take the form of output to a screen: graphics, text, output to a sound device, printed documents or data output to another program. For this unit you need to be familiar with a few input and output commands. The little black box that appears on your screen is called the console. In VB.NET all the commands to read and write from this are accessed from the console. command, let's take a look at some: Outputs For the AS course it is unlikely you will need anything beyond the print to screen command and the write to file command (see later). There are two write to screen commands that you should be familiar with: console.write("Hello") 'writes the word hello to the screen console.writeline("Hello") 'writes the word Hello to the screen and adds a carriage return (new line) Let's see an example of this in action: console.write("Hello ") console.write("how ") console.write("are ") console.writeline("you?") console.writeline("I'm fine thank ") console.write("you.") This would output the following: Hello how are you? I'm fine thank you. Notice the difference between a writeline and a write command. Extension: Console methods We can do a lot of things with the console command. If you are using Visual Studio then type the following: console. Up should pop some suggestions. Play around with BackgroundColor and ForegroundColor There is also a command to output a small and annoying sound, it's unlikely you'll need to know this for the exam, and your teachers will most likely hate it. console.beep() 'plain beep console.beep(2000,500) 'beep at 2000Hz for 0.5 seconds Find out more about the console command on the MSDN website Inputs To make your program interactive you'll need your user to input commands, for the exam these will most likely be text instructions or reading from a file (covered later). You might look at buttons and games controllers next year. In VB.NET there are two types of input command that you need to know: variable1 = console.readline() 'reads input until user presses enter and stores it in variable1 variable2 = console.read() 'reads one key press/character and stores the ASCII code in variable2. We'll learn more about this later Let's take a look at a quick example of where this might be used: dim name as string 'declare a variable called name console.write("Please insert your name:") ' write "Hello" and the name to the screen name = console.readline() 'assign the user's input into the variable name console.writeline("Hello " & name) ' write "Hello" and the name to the screen Please insert you name: Ali Hello Ali There is also the console.ReadKey()command that reads in a single character. Take a look at this example: dim urChoice as char 'declare the name console.writeline("Please select from options 1,2,3 or 4:") urChoice = console.Readline() 'read the users input into the variable name console.writeline("You chose : " & urChoice ) Please select from options 1,2,3 or 4: 4 You chose : 4 Exercise: Inputs and Outputs What does the following code output: console.writeline("The ") console.write("Cat") console.write("sat ") console.writeline("on ") console.writeline("the " & "mat") The Catsat on the mat dim num as integer = 19 console.writeline("The average age ") console.write("of a combat soldier ") console.write("in Vietnam was " & num) The average age of a combat soldier in Vietnam was 19 Write code to display the following to the screen: My favourite colours: Red Blue console.writeline("My favourite colours:") console.writeline("Red") console.writeline("Blue") What would the following look like: dim age as string dim name as integer console.writeline("Enter your name: ") age = console.readline() console.writeline("Enter your age: ") name = console.readline() console.writeline("Hello " & name & ". You are " & age & " years old ") for the input: John 16 Enter your name: John Enter your age: 16 Hello 16. You are John years old Whoops! Fix this: dim age as integer dim name as string console.writeline("Enter your name: ") name = console.readline() console.writeline("Enter your age: ") age = console.readline() console.writeline("Hello " & name & ". You are " & age & " years old ")