HP OpenVMS Systems Documentation
HP BASIC for OpenVMS
BASIC lets you explicitly assign a data type to a variable or an array. For example:
DECLARE DOUBLE Interest_rate
Data type keywords are described in Section 1.4. For more information
about explicit declaration of variables, see the COMMON, DECLARE,
DIMENSION, DEF, FUNCTION, EXTERNAL, MAP, and SUB statements in
1.5.4 Subscripted Variables and Arrays
A subscripted variable references part of an array. Arrays can be of any valid data type. Subscripted variables and arrays follow the same naming conventions as unsubscripted variables. Subscripts follow the variable name in parentheses and define the variable's position in the array. When you create an array, you specify the maximum size of the array (the bounds) in parentheses following the array name.
In Example 1-2, the DECLARE statement sets the bounds of the arrayemp_name to 1000. Therefore, the maximum value for an emp_name subscript is 1000. The bounds of the array define the maximum value for a subscript of that array.
|Example 1-2 Using the DECLARE Statement to Set Array Boundaries|
DECLARE STRING emp_name(1000) FOR I% = 0% TO 1000% INPUT "Employee name";emp_name(I%) NEXT I%
An array is a set of data ordered in one or more dimensions. A one-dimensional array, like emp_name(1000), is called a list or vector. A two-dimensional array, like payroll_data(5,5), is called a matrix. An array of more than two dimensions, like big_array(15,9,2), is called a tensor.
As a default, BASIC arrays are always zero-based. The number of elements in any dimension includes element number zero. For example, the array emp_name contains 1001 elements because BASIC allocates element zero. Payroll_data(5,5) contains 36 elements because BASIC allocates row and column zero.
Often, however, applications call for arrays that are not zero-based. In BASIC, you can define arrays that are not zero-based by specifying a lower bound, as well as an upper bound, for the subscripts. In this way, you can create an array with arbitrary starting and ending points. For example, you might want to create array birth_rate that holds the annual birth rate statistics for the years 1950 to 1985:
DECLARE birth_rate(1950 TO 1985)
Lower bounds are not allowed with virtual arrays or arrays used in MAT statements. If a multidimensional array is declared with lower bounds specified for some dimensions and not others, zero will be used for those dimensions without lower bounds.
You can use the UBOUND and LBOUND functions to determine the upper and lower bounds of an array. For a description of these functions, see Chapter 3.
For all arrays except virtual arrays, the total number of array elements cannot exceed 2147483647. Note, however, that this is a theoretical value; the actual maximum size of an array that you can declare depends on the configuration of your system.
BASIC arrays can have up to 32 dimensions. You can specify the type of data the array contains with data type keywords. See Table 1-2 for a list of BASIC data types.
A(6%) B (6%) C$ (6%)
A(6%) refers to the seventh item in this list:
A(0%) A(1%) A(2%) A(3%) A(4%) A(5%) A(6%)
An element in a two-dimensional array has two subscripts, in parentheses, following the variable name. The first subscript specifies the row number and the second subscript specifies the column number. Use a comma to separate the subscripts. You may optionally put a space between the array name and the subscripts. For example:
A (7%,2%) A%(4%,6%) A$ (10%,10%)
In Figure 1-1, the arrow points to the element specified by the subscripted variable A%(4%,6%).
Figure 1-1 Representation of the Subscript Variable A%(4%,6%)
Although a program can contain a variable and an array with the same name, this is poor programming practice. Variable A and the array A(3%,3%) are separate entities and are stored in completely separate locations, so it is a good idea to give them different names.
Note that a program cannot contain two arrays with the same name but a different number of subscripts. For example, the arrays A(3%) and A(3%,3%) are invalid in the same program.
BASIC arrays can be redimensioned at run time. See the HP BASIC for OpenVMS User Manual for
more information about arrays.
1.5.5 Initialization of Variables
BASIC generally sets variables to zero or null values at the start of program execution. Variables initialized by BASIC include:
A constant is a numeric or character literal that does not change during program execution. A constant may optionally be named and associated with a data type. BASIC allows the following types of constants:
A constant of any of the above data types can be named with the DECLARE CONSTANT statement. You can then refer to the constant by name in your program. See Section 1.6.3 for information about naming constants.
You can use the OPTION statement to declare a default data type for all constants in your program. This statement allows you to specify a data type for only the constants in your program; you can specify a different data type for variables. You can also use a special numeric literal notation to specify the value and data type of a numeric literal. Numeric literal notation is discussed in Section 1.6.4.
If you do not specify a data type for a numeric constant with the DECLARE CONSTANT statement or with numeric literal notation, the type and size of the constant is determined by the default REAL, INTEGER, or DECIMAL type set with the BASIC DCL command or the OPTION statement.
To simplify the representation of certain ASCII characters and mathematical values, BASIC also supplies some predefined constants.
The following sections discuss numeric and string constants, named
constants, numeric literal notation, and predefined constants.
1.6.1 Numeric Constants
A numeric constant is a literal or named constant whose value never changes. In BASIC, a numeric constant can be a floating-point number, an integer, or a packed decimal number. The type and size of a numeric constant is determined by the following:
DECLARE BYTE CONSTANT age = 12
This example associates the numeric literal 12 and the BYTE data type
with the identifier age. To specify a data type for an unnamed
numeric constant, you must use the numeric literal notation format
described in Section 1.6.4.
126.96.36.199 Floating-Point Constants
A floating-point constant is a literal or named constant with one or more decimal digits, either positive or negative, with an optional decimal point and an optional exponent (E notation). If the default data type is integer, BASIC will treat the literal as an INTEGER unless it contains a decimal point or the character E. If the default data type is DECIMAL, an E is required or BASIC treats the literal as a packed decimal value.
Table 1-3 contains examples of floating-point literals with REAL, INTEGER, and DECIMAL default data types.
Very large and very small numbers can be represented in E (exponential) notation. To indicate E notation, a number must be followed by the letter E (or e). It also must be followed by an exponent sign and an exponent. The exponent sign indicates whether the exponent is positive or negative and is optional only if you are specifying a positive exponent. The exponent is an integer constant (the power of 10).
See Table 1-2 for decimal-place precision of floating-point keywords.
Table 1-4 compares numbers in standard and E notation.
|Standard Notation||E Notation|
The range and precision of floating-point constants are determined by
the current default data types or the explicit data type used in the
DECLARE CONSTANT statement. However, there are limits to the range
allowed for numeric data types. See Table 1-2 for a list of BASIC
data types and ranges. BASIC signals the fatal error "Floating
point error or overflow" (ERR=48) when your program attempts to
specify a constant value outside of the allowable range for a
floating-point data type.
188.8.131.52 Integer Constants
An integer constant is a literal or named constant, either positive or negative, with no fractional digits and an optional trailing percent sign (%). The percent sign is required for integer literals only if the default type is not INTEGER.
In Table 1-5, the values are all integer constants. The presence of the percent sign varies depending on the default data type.
The range of allowable values for integer constants is determined by either the current default data type or the explicit data type used in the DECLARE CONSTANT statement. Table 1-2 lists BASIC data types and ranges. BASIC signals an error for a number outside the applicable range.
If you want BASIC to treat numeric literals as integer numbers, you must do one of the following:
You cannot use percent signs in integer constants that appear in DATA statements. Doing so causes BASIC to signal "Data format error" (ERR=50).
A packed decimal constant is a number, either positive or negative, that has a specified number of digits and a specified decimal point position (scale). You specify the number of digits (d) and the position of the decimal point (s) when you declare the constant as a DECIMAL(d,s). If the constant is not declared, the number of digits and the position of the decimal is determined by the representation of the constant.
For example, when the default data type is DECIMAL, 1.234 is a
DECIMAL(4,3) constant, regardless of the default decimal size.
Likewise, using numeric literal notation, "1.234"P is a
DECIMAL(4,3) constant, regardless of the default data type and default
DECIMAL size. Numeric literal notation is described in Section 1.6.4.
1.6.2 String Constants
You can embed double quotation marks within single quotation marks ('this is a "text" string') and vice versa ("this is a 'text' string"). Note, however, that BASIC does not accept incorrectly paired quotation marks and that only the outer quotation marks must be paired. For example, the following character strings are valid:
"The record number does not exist." "I'm here!" "The terminating 'condition' is equal to 10." "REPORT 543"
However, the following strings are not valid:
"Quotation marks that do not match' "No closing quotation mark
Characters in string constants can be letters, numbers, spaces, tabs, 8-bit data characters, or the NUL character (ASCII code 0). If you need a string constant that contains a NUL, you should use CHR$(NUL). See Section 1.6.4 for information about explicit literal notation.
Note that NUL is a predefined integer constant. See Section 1.6.5.
The compiler determines the value of the string constant by scanning all its characters. For example, because of the number of spaces between the delimiters and the characters, these two string constants are not the same:
" END-OF-FILE REACHED " "END-OF-FILE REACHED"
BASIC stores every character between delimiters exactly as you type it into the source program, including:
The delimiting quotation marks are not printed when the program is executing. The value of the string constant does not include the delimiting quotation marks. For example:
PRINT "END-OF-FILE REACHED" END
BASIC does, however, print double or single quotation marks when they are enclosed in a second paired set. For example:
PRINT 'FAILURE CONDITION: "RECORD LENGTH"' END
FAILURE CONDITION: "RECORD LENGTH"
BASIC allows you to name constants. You can assign a name to a constant that is either internal or external to your program and refer to the constant by name throughout the program. This naming feature is useful for the following reasons:
You can use named constants anywhere you can use a constant, for example, to specify the number of elements in an array.
You cannot change the value of an explicitly named constant during
184.108.40.206 Naming Constants Within a Program Unit
You name constants within a program unit with the DECLARE statement, as is shown in Example 1-3.
|Example 1-3 Naming Constants Within a Program Unit|
DECLARE DOUBLE CONSTANT preferred_rate = .147 DECLARE SINGLE CONSTANT normal_rate = .162 DECLARE DOUBLE CONSTANT risky_rate = .175 . . . new_bal = old_bal * (1 + preferred_rate)^years_payment
When interest rates change, only three lines have to be changed rather than every line that contains an interest rate constant.
Constant names must conform to the rules for naming internal, explicitly declared variables listed in Section 1.5.1.
The value associated with a named constant can be a compile-time expression as well as a literal value, as shown in Example 1-4.
|Example 1-4 Associating Values with Named Constants|
DECLARE STRING CONSTANT Congrats = & "+--------------------+" + LF + CR + & "| Congratulations! |" + CR + CR + & "+--------------------+" . . . PRINT Congrats . . . PRINT Congrats
Named constants can save you programming time because you do not have to retype the value every time you want to display it.
Valid operators in DECLARE CONSTANT expressions include string concatenations and all valid arithmetic, relational, and logical operators except exponentiation. You cannot use built-in functions in DECLARE CONSTANT expressions.
BASIC allows constants of all data types except RFA to be named constants. Because you cannot declare a constant of the RFA data type, you cannot name a constant of that type.
You can specify only one data type in a DECLARE CONSTANT statement. To
declare a constant of a different data type, you must use a second
DECLARE CONSTANT statement.
220.127.116.11 Naming Constants External to a Program Unit
To declare constants outside the program unit, use the EXTERNAL statement, as shown in Example 1-5.
|Example 1-5 Declaring Constants Outside the Program Unit|
EXTERNAL LONG CONSTANT SS$_NORMAL EXTERNAL WORD CONSTANT IS_SUCCESS
The first line declares the OpenVMS status code SS$_NORMAL to be an external LONG constant. The second line declares IS_SUCCESS, a success code, to be an external WORD constant. Note that BASIC allows only external BYTE, WORD, LONG, QUAD, and SINGLE constants. The OpenVMS Linker supplies the values for the constants specified in EXTERNAL statements.
In BASIC, the named constant might be a system status code or a global
constant declared in another OpenVMS layered product.
1.6.4 Explicit Literal Notation
[radix] "num-str-lit" [data-type]
|D||Decimal (base 10)|
|B||Binary (base 2)|
|O||Octal (base 8)|
|X||Hexadecimal (base 16)|
The BASIC default radix is decimal. Binary, octal, and hexadecimal notation allow you to set or clear individual bits in the representation of an integer. This feature is useful in forming conditional expressions and in using logical operations. The ASCII radix causes BASIC to translate a single ASCII character to its decimal equivalent. This decimal equivalent is an INTEGER value; you specify whether the INTEGER subtype should be BYTE, WORD, LONG, or QUAD.
Num-str-lit is a numeric string literal. It can be the digits 0 and 1 when the radix is binary, the digits 0 to 7 when the radix is octal, the digits 0 to F when the radix is hexadecimal, and the digits 0 to 9 when the radix is decimal. When the radix is ASCII, num-str-lit can be any valid ASCII character.
The following are examples of explicit literals:
|D"255"L||Specifies a LONG decimal constant with a value of 255|
|"4000"F||Specifies a SINGLE decimal constant with a value of 4000|
|A"M"L||Specifies a LONG integer constant with a value of 77|
|A"m"B||Specifies a BYTE integer constant with a value of 109|
A quoted numeric string alone, without a radix and a data type, is a string literal, not a numeric literal. For
|"255"||Is a string literal|
|"255"W||Specifies a WORD decimal constant with a value of 255|
If you specify a binary, octal, ASCII, or hexadecimal radix, data-type must be an integer. If you do not specify a data type, BASIC uses the default integer data type. For example:
|B"11111111"B||Specifies a BYTE binary constant with a value of -1|
|B"11111111"W||Specifies a WORD binary constant with a value of 255|
|B"11111111"||Specifies a binary constant of the default data type (BYTE, WORD, LONG, or QUAD)|
|B"11111111"F||Is illegal because F is not an integer data type|
|X"FF"B||Specifies a BYTE hexadecimal constant with a value of -1|
|X"FF"W||Specifies a WORD hexadecimal constant with a value of 255|
|X"FF"D||Is illegal because D is not an integer data type|
|O"377"B||Specifies a BYTE octal constant with a value of -1|
|O"377"W||Specifies a WORD octal constant with a value of 255|
|O"377"G||Is illegal because G is not an integer data type|