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6. Variables

A variable must be declared before it can be used, otherwise an undefined name error will be generated. A variable is declared using the variable keyword, e.g,

      variable x, y, z;
declares three variables, x, y, and z. This is an example of a variable declaration statement, and like all statements, it must end in a semi-colon.

Variables declared this way are untyped and inherit a type upon assignment. The actual type checking is performed at run-time. For example,

        x = "This is a string";
        x = 1.2;
        x = 3;
        x = 2i;
results in x being set successively to a string, a float, an integer, and to a complex number (0+2i). Any attempt to use a variable before it has acquired a type will result in an unitialized variable error.

It is legal to put executable code in a variable declaration list. That is,

         variable x = 1, y = sin (x);
are legal variable declarations. This also provides a convenient way of initializing a variable.

Variables are classified as either global or local. A variable declared inside a function is said to be local and has no meaning outside the function. A variable is said to be global if it was declared outside a function.

The following global variables are predefined by the language and are mainly used as convenience variables:

      $0 $1 $2 $3 $4 $5 $6 $7 $8 $9

An intrinsic variable is another type of global variable. Such variables have a definite type which cannot be altered. Variables of this type may also be defined to be read-only, or constant variables. An example of an intrinsic variable is PI which is a read-only double precision variable with a value of approximately 3.14159265358979323846.

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