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Defining (symbolic) constants in a computer program

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• Symbolic constants
  • Symbolic constants:

    Symbolic constants = identifiers that represents a numeric value (or a character)

    Example:

    π = 3.1415926.....

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• The EQU assembler directive
  • Syntax:

    label EQU constant

    Effect:

    tell the assembler to set the symbolic name label equal to the value of the constant constant

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  • Label: (similar to an identifier in high level prog language)

    a label consists of letters, digits and _ (underscore) a label must begin with a letter Additional rule: The first character of the label must start at column 1 of the test        or The label must be end in a colon (:)

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  • Examples:

    First column position in file | V MAX EQU 100 - good EQU directive MAX: EQU 100 - good EQU directive MAX: EQU 100 - good EQU directive MAX EQU 100 - BAD EQU directive --- error !!

    The 3 correct directives will:

    define the symbol MAX to be equal (= same as) the constant 100

    Note:

    In Java, we define the above symbolic constant MAX using the following construct: final int MAX = 100 ;

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• Using symbolic constants
  • Using a symbolic constant:

    After you have defined a symbolic constant MAX, then: All occurences of the symbol MAX will be replaced by the defined constant (i.e. 100)

    This is a simple concept, just like in Java.

    So I won't dwell on it any longer....