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Storing (your own) non-numerical information inside a computer memory

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• Storing your own type of information
  • Problem statement:

    Suppose we want to store information of people's gender and marital status in a computer program

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  • Problem:

    The computer memory can only store binary patterns (= binary numbers) Binary numbers are not the same as information

    $64,000 question:

    How do we bridge the gap between code (= binary numbers) and information ???

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• Representating information
  • How to represent information:

    Code + Context = Information            I.e.: information is represented by a code by agreeing on a context to interpret a code

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  • Example:

    We encode the gender information of persons as follows: 0 = male 1 = female I.e.: we agree that when storing "gender" information, we use 0 to represent "male" and 1 to represent "female" Furthermore, we encode the marital status information of persons as follows: 0 = single 1 = married 2 = divorse 3 = widowed Can you read (= understand) this information about these 2 persons: Person ----------------------- JJ 0 0 JM 0 1 Answer: no because we do not have the context for the code value 0, 1 Can you read (= understand) this information about these 2 persons now: Person MaritalStatus Sex ------------------------------- JJ 0 0 JM 0 1 Answer: JJ: single male JM: single female

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• An English example to show you the importance of context
  • Question:

    Make a correct English sentence that begins with:             You is ....

    I'll give you the answer in class.

    Hint: if you have a hard time coming up with a correct sentence, then you have been using "you" as a personal pronoun

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    The context of the word usage will determine how you interpret the information convey by a word !!!

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• Representing information inside a computer
  • Where in a computer program is information stored ?

    Information are stored in the program variables !!!

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  • How to store information inside a computer program:

    The data type of a variable convey the context used to decipher the value (= number) stored in the variable Each data type uses its own information encoding method !!!    (More detail below) The information is encode as binary number patterns and stored in the program variable Example: char letter; int number; letter = 65; // The value 65 in char type // represents the letter 'A' number = 65; // The value 65 in int type // represents the number 65

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• Codes used to represent information stored inside the computer
  • Fact:

    Different types of information are represented by different codes !!!

    Example:

    Textual information: encoded using the ASCII code           (Or the Unicode in case of non-English language)             Unsigned integer values: encoded using the binary number system           Signed integer values: encoded using the 2's complement code           Single-precision floating number values: encoded using the "Binary32" IEEE 754 code           See: click here Double-precision floating number values: encoded using the "Binary64" IEEE 754 code           See: click here

    We will discuss these code later in the course.