Chapter 2: Data Types, Variables

This chapter explains the DISGCL data types and shows how to specify constants and variables.

2.1 Data Types

As described in the last chapter, DISGCL data can have the following types:

     ---------------------------------------------------
     |  Type   |  Bytes  |           Range             |
     ---------------------------------------------------
     | CHAT    |    1    |      -128   -  127          |
     ---------------------------------------------------
     | BYTE    |    1    |         0   -  255          |
     ---------------------------------------------------
     | SHORT   |    2    |    -32768   -  32767        |
     ---------------------------------------------------
     | INT     |    4    | -2147483648 -  2147483647   |
     ---------------------------------------------------
     | FLOAT   |    4    |     1.2E-38 -  3.4E+38      |
     ---------------------------------------------------
     | DOUBLE  |    8    |    2.2E-308 -  1.8E+308     |
     ---------------------------------------------------
     | COMPLEX |    8    |     1.2E-38 -  3.4E+38      |
     ---------------------------------------------------
     | STRING  |  n + 1  |                             |
     ---------------------------------------------------
                    Figure 2.1: Data Types

All data in DISGCL are variables or constants. As in other programming languages, variables can change their values during the lifetime of a DISGCL session. But in DISGCL, variables can also change their types, and they don't have to be declared.

The following rules are applied to variables:

The first character must be a letter. Other characters can be letters, digits, or underscores.
The first 16 characters of variable names are significant.
DISGCL is not case-sensitive. Variable names, keywords, functions, routines and parameters can be specified in uppercase and lowercase letters.

2.3 System Variables

System variables are special variables with a predefined meaning. For example, system variables can be used to set options for quick plots. System variables begin with the '%' character and are available to all DISGCL units such as subroutines and functions.

2.4 Specifying Constants

Constants are data that cannot change their values during the life of a DISGCL session. Constants can be integers, floating point numbers and strings.

Integer constants can be specified in decimal or hexadecimal notation. Floating point constants contain a decimal point and can have an exponential part preceded by e or E. String constants must be enclosed in a pair of either apostrophes or quotation marks. Complex constants contain the keyword 'COMPLEX' and a real and imaginary part. The imaginary part is optional and assumed to be zero if it is omitted.

Examples:

           ----------------------------------
           |   Constant    |     Type       |
           ----------------------------------
           |     120       |    Decimal     |
           ----------------------------------
           |     0xFF      |  Hexadecimal   |
           ----------------------------------
           |     0.56      | Floating point |
           ----------------------------------
           |    3.6E2      | Floating point |
           ----------------------------------
           |    "ABC"      |     String     |
           ----------------------------------
           |    'abc'      |     String     |
           ----------------------------------
           | COMPLEX (3,4) |    COMPLEX     |
           ----------------------------------
           | COMPLEX (7)   |    COMPLEX     |
           ----------------------------------
                Figure 2.2: Constants

2.5 Arrays

An array is a collection of data that share the same type and a common name. Array elements can be accessed by specifying subscripts in square brackets.

Examples:

A[i] = 5
B[i, j] = 8

There are several ways to create arrays in DISGCL:

If an expression is assigned to a variable and the value of the expression is an array, the variable will also be an array.
The DISGCL commands CHAR, BYTE, SHORT, INT, FLOAT, DOUBLE and COMPLEX create corresponding arrays and initialize them with zeros. Example:
```
INT A[10], B[20,10] 
```
Integer and floating point arrays can be created and initialized with the statement:
vray = { list }
where list is a constant list of integers or floating point numbers separated by commas.

Additional notes:

Array subscripts begin with the number 0.
If a subscript is out of range, DISGCL prints a warning and cancels the calculation.
Multidimensional arrays are stored by rows.
If a subscript appears in a string, the string element is handled as an integer where the value of the integer is the ASCII code of the string element.

2.6 Subscripts

Subscripts can be used to access single array elements or sections of arrays. The following are examples of array subscripts:

   A[i]         Element i of array A
   A[i:j]       Array section of size j - i + 1
   B[i1:i2, j]  Elements i1 to i2 of column j
   B[:i2, j]    Elements 0 to i2 of column j
   B[i1:, j]    Elements i1 to m - 1 of column j
   B[*, j]      The whole column j.

2.7 Character Arrays and Strings

Strings in DISGCL are stored as character arrays terminated with ASCII value zero. Normally, strings and character arrays can be used in the same way if character arrays contain a string terminator. Some I/O functions require character arrays instead of strings to store characters. Character arrays can be defined with the CHAR command.

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