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The (only) way that humans and computers communicate with each other

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• Communication between a human and a computer
  • Communication:

    Communication is a 2 way process: Input (into the computer): How does a human enter inputs to a computer ??         Output (from the computer): How does a computer print outputs so a human can see (and understand) them ??

    Communication between humans and computers are facilitated by special input and output devices

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  • Input/output devices:

    Input device = a device that enable a human to transmit data to a computer Examples: Output device = a device that enable a computer to transmit data to a human Examples:

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• Methodology of human/computer communication
  • Every input/output device used in human/computer communication follow the following methodology:

    Each input device has a pre-defined set of codes that represent the possible input values that a human can enter The input device transmits the pre-defined code to the computer that represents a certain input Each output device has a pre-defined set of codes that represent the possible output values that a human can receive The computer sends a code to the output device and the output device converts the code into human-visible information

    I will discuss the communication methodology using the key board and terminal as examples (see below)

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• Most commom communication method between humans and computer
  • Most commonly used communication method between a human and a computer:

    Most commonly used input device: key board Most commonly used output device: Monitor

    I will now illustrate the communication methodology using the key board and terminal as examples

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• Code used in key board/terminal in the human/computer communication
  • Code used in key board and (text) terminal devices:

    ASCII code or Unicode

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  • Before the introduction of the Unicode:

    Key boards and terminal use the ASCII code

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  • Nowadays:

    Some devices (e.g., using US keyboards) that only allow English-inputs still use ASCII code Many (advanced) devices (e.g., tablets, phones) use Unicode

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• How user enters text inputs into the computer (using keyboard)
  • How a user enters 'H' to the computer:

    Explanation:

    The user looks for a key that has the symbol 'H' on the key board When the user presses the 'H' key on the keyboard input: The keyboard is wired in such a way that when the 'H' key is pressed, it will transmit the ASCII code 01001000 (= 72 decimal) that represents the character 'H' to the computer.

    I like to give you an evidence that the key board transmits ASCII codes to the computer

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• Evidence that the key board transmits ASCII code to the computer
  • In CS170/CS171, you were told to use Java.util.Scanner to reading integer from the input.

    Your Java programs would contain these lines:

    import java.util.Scanner; // Import class from Java library ... Scanner in = new Scanner( System.in ); // Create Scanner object using the System.in object !!

    The System.in object in Java is associated with the key board.

    The reason that you use System.in to create a Scanner object is so that the Scanner object will read from the key board

    (You may have learned to use Scanner on an File object to read a data file.

    Just than you know that: whatever object you use to create the Scanner object, it will read input from that object.)

    The Scanner object contains methods to convert ASCII representation to 2's complement representation.

    So what we do now is show you Java input without using Scanner:

    We will read input using only the System.in (key board) object !!!

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  • Consider the following Java program that only uses System.in for input:

    // File: /home/cs255001/demo/atoi/JavaInput_1.java // // Demo reading input WITHOUT using Scanner utility class !!!! // public class JavaInput_1 { public static void main(String[] args) throws Exception { byte[] b = new byte[100]; int count; while ( true ) { System.out.print("Enter input: "); count = System.in.read(b); // Read from key board System.out.println("# characters read = " + count); for (int i = 0; i < count; i++) System.out.println(b[i]); System.out.println("\n"); } } }

    The method call System.in.read(b) will read an input line (until you hit <RETURN> key) and store it in the byte[] array b,

    The method System.in.read(b) returns the number of characters in the input.

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  • Here's an sample execution (using the inputs "12<ENTER>" and "123<ENTER>"):

    cheung@aruba> java JavaInput_1 Enter input: 12 # characters read = 3 49 50 10 Enter input: 123 # characters read = 4 49 50 51 10

    When you enter 12<ENTER>, the input values are: 49 50 10 because:

    49 is the ASCII code for the character '1' 50 is the ASCII code for the character '2' 10 is the ASCII code for the character NEWLINE (ENTER)

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• File fact: computer store text file internally using the ASCII code

  • FACT: Text files use the ASCII code to encode/represent characeters in the text files.

    (This fact is easier to explain with a live demo (where I point out to you what to look for and where to look at) and I will demo this in class - so if you don't come to class, you will miss out on some stuff even most of the material are in webpages)

    In other words: when we want to print text messages to a terminal, the output context is always ASCII code

  • Text stored in a data file is also encoded in ASCII

    Try doing this experiment:

    Edit a file Execute: od -c filename to see the content in "text" form Execute: od -b filename to see the content in "octal ASCII code" form Execute: /home/cs255001/demo/atoi/dumpint filename to see the content in "decimal ASCII code" form

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• How the terminal display text outputs to the human (user)
  • How a computer displays 'H' to a human:

    Note: what is actually happening is the following:

    (The computer does not know that it wants to display the letter 'H' !!! The letter 'H' is represented inside the computer by the ASCII code 01001000 (= 72 decimal) The computer wants to show the character that is represented by 01001000 to the human (user)

    How the computer "communicate" 01001000 ('H') to a human:

    The computer sends 01001000 to the terminal When the terminal receives the ASCII code 01001000: The terminal is wired in such a way that it will paint this "picture" on a portion of the screen: H

    use

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• Very important lesson learned
  • Important fact:

    The key board always uses the ASCII codes to convey information from human user to the computer The terminal always uses the ASCII codes to convey information from the computer to the human user

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  • That means:

    Text information Representation in ASCII code (binary) --------------------+------------------------------------------------ H 01001000 He 01001000 01100101 Hello 01001000 01100101 01101100 01101100 01101111

    But also:

    Text information Representation in ASCII code (binary) --------------------+------------------------------------------------ 1 00110001 12 00110001 00110010 123 00110001 00110010 00110011

    Try it for yourself:

    Enter a number:    12 The key board will send these binary ASCII code to the computer as input:    0100100001100101011100100110010100100000011000100110010100100000011100110110010101100011011100100110010101110100001000000110110101100101011100110111001101100001011001110110010101110011001000010010000100110001 Made by @mathias ---- GitHub! source