HP OpenVMS Systems Documentation

OpenVMS User's Manual

When you compare two character strings, the strings are compared character by character. Strings of different lengths are not equal (for example, "dogs" is greater than "dog").

The comparison criteria are the ASCII values of the characters. Under these criteria, the digits 0 to 9 are less than the uppercase letters A to Z, and the uppercase letters A to Z are less than the lowercase letters a to z. A character string comparison ends when either of the following conditions is true:

• All the characters have been compared, in which case the strings are equal.
• The first mismatch occurs.

Table 12-1 lists different types of string comparisons.

In all of the following examples, assume that the symbol LAST_NAME has the value "WHITFIELD".

• In the following example, the symbol TEST_NAME is evaluated as 0 (False); the value of the symbol LAST_NAME does not equal the literal "HILL":

  $ TEST_NAME = LAST_NAME .EQS. "Hill" $ SHOW SYMBOL TEST_NAME TEST_NAME = 0 ...

• In the following example, the symbol TEST_NAME is evaluated as 1 (True); the value of the symbol LAST_NAME is greater than or equal to the literal "HILL":

  $ TEST_NAME = LAST_NAME .GES. "HILL" $ SHOW SYMBOL TEST_NAME TEST_NAME = 1 ...

• In the following example, the symbol TEST_NAME is evaluated as 1 (True); the value of the symbol LAST_NAME is greater than the literal "HILL.":

  $ TEST_NAME = LAST_NAME .GTS. "HILL" $ SHOW SYMBOL TEST_NAME TEST_NAME = 1 ...

• In the following example, the symbol TEST_NAME is evaluated as 0 (False); the value of the symbol LAST_NAME is not less than or equal to the literal "HILL":

  $ TEST_NAME = LAST_NAME .LES. "HILL" $ SHOW SYMBOL TEST_NAME TEST_NAME = 0 ...

• In the following example, the symbol TEST_NAME is evaluated as 0 (False); the value of the symbol LAST_NAME is not less than the literal "HILL":

  $ TEST_NAME = LAST_NAME .LTS. "HILL" $ SHOW SYMBOL TEST_NAME TEST_NAME = 0 ...

• In the following example, the symbol TEST_NAME is evaluated as 1 (True); the value of the symbol LAST_NAME does not equal the literal "HILL":

  $ TEST_NAME = LAST_NAME .NES. "HILL" $ SHOW SYMBOL TEST_NAME TEST_NAME = 1 ...

You can replace part of a character string with another character string by specifying the position and size of the replacement string. The format for local symbols is:

The format for global symbols is:

The elements are as follows:

To replace substrings, observe the following rules:

• The square brackets are required notation. No spaces are allowed between the symbol name and the left bracket.
• Integer values for size and offset values can range from 0 to 768.
• The replacement string must be a character string.
• The symbol name you specify can be undefined initially. The assignment statement creates the symbol name and if necessary, provides leading or trailing spaces in the symbol value.
• You can specify an offset and size to create a symbol that represents a blank line.

Lining up records in columns makes a list easier to read and sort. You can use this format to specify how you want data to be stored.

In the following example, the first assignment statement gives the symbol A the value PACKRAT. The second statement specifies that MUSK replace the first four characters in the value of A. The result is that the value of A becomes MUSKRAT.

$ A := PACKRAT
$ A[0,4] := MUSK
$ SHOW SYMBOL A
   A = "MUSKRAT"

In the following example, the symbol B does not have a previous value, so it is given a value of four leading spaces followed by RAT:

$ B[4,3] := RAT

In the following example, a value of 80 blank spaces is assigned to the symbol LINE:

$ LINE[0,80]:= " "

In the following example, the first statement fills in the first 15 columns of DATA with whatever value NAME has. The second statement fills in column 18 with whatever value GRADE has. Columns 16 and 17 contain blanks:

$ DATA[0,15] := 'NAME'
$ DATA[17,1] := 'GRADE'

A number can have the following values:

• Decimal --- the ASCII characters 0 to 9
• Hexadecimal --- the ASCII characters 0 to 9 and A to F
• Octal --- the ASCII characters 0 to 7

The number you assign to a symbol must be in the range --2147483648 to 2147483647 (decimal). An error is not reported if a number outside this range is specified or calculated but an incorrect value results.

12.7.1 Specifying Numbers

At DCL command level and within command procedures, specify a number as follows:

• Positive numbers
  Specify a positive number by typing the appropriate digits.
• Negative numbers
  Precede a negative number with a minus sign ( - ).
• Radix
  Specify a number in a radix other than decimal by preceding the number (but not the minus sign) with %X for hexadecimal numbers and %0 for octal numbers.
• Fractions
  A number cannot include a decimal point. In calculations, fractions are truncated. For example, 8 divided by 3 equals 2.

In the following example, the number 13 is assigned to the symbol DOG_COUNT:

$ DOG_COUNT = 13
$ SHOW SYMBOL DOG_COUNT
  DOG_COUNT = 13   Hex = 0000000D  Octal = 00000000015

In the following example, the negative number ( -15237 ) is represented with a minus sign ( - ):

$ BALANCE = -15237
$ SHOW SYMBOL BALANCE
  BALANCE = -15237   Hex = FFFFC47B  Octal = 37777742173

In the following example, the hexadecimal number D is represented with the prefix %X:

$ DOG_COUNT = %XD
$ SHOW SYMBOL DOG_COUNT
  DOG_COUNT = 13   Hex = 0000000D  Octal = 00000000015
$ BALANCE = -%X3B85
$ SHOW SYMBOL BALANCE
  BALANCE = -15237   Hex = FFFFC47B  Octal = 37777742173

Numbers are stored internally as signed 4-byte integers, called longwords; positive numbers have values of 0 to 2147483647 and negative numbers have values of 4294967296 minus the absolute value of the number. The number -15237 , for example, is stored as 4294952059. Negative numbers are converted back to minus-sign format for ASCII or decimal displays; however, they are not converted back for hexadecimal and octal displays. For example, the number -15237 appears in displays as hexadecimal FFFFC47B (decimal 4294952059) rather than hexadecimal --00003B85.

Numbers are stored in text files as a series of digits using ASCII conventions (for example, the digit 1 has a storage value of 49).

In a numeric expression, the values involved must be literal numbers (such as 3) or symbols with numeric values. In addition, you can use a character string that represents a number (for example, "23" or " -51 "). If you perform an operation or comparison between a number and a character string, DCL converts the character string to a number.

Numeric expressions combine the following values (called integer operands):

• Integers. For example:

  $ COUNT = 1

• Lexical functions that are evaluated as integers. For example:

  $ B = F$INTEGER("-9" + 23)

• Symbols that have integer values. For example:

  $ A = B - 6

  
  In the preceding example, the symbol B represents the integer value returned by the F$INTEGER function ( -923 ).

These integer operands can be connected by arithmetic, logical, and comparison operators, as described in the following sections.

12.7.3 Performing Arithmetic Operations

You can specify the following arithmetic operations:

• Multiplication
  The asterisk (*) multiplies two numbers.
• Division
  The slash (/) divides the first specified number by the second specified number. If a number does not divide evenly, the remainder is lost. No rounding takes place.
• Addition
  The plus sign (+) adds two numbers.
• Subtraction
  The minus sign (-) subtracts the second specified number from the first specified number.
• Unary plus and minus
  The plus and minus signs change the sign of the number they precede.

Examples

• The following example demonstrates using multiplication when assigning a symbol:

  $ BALANCE = 142 * 14 $ SHOW SYMBOL BALANCE BALANCE = 1988 Hex = 000007C4 Octal = 00000003704

• The following example demonstrates using division when assigning a symbol:

  $ BALANCE = BALANCE / 14 $ SHOW SYMBOL BALANCE BALANCE = 142 Hex = 0000008E Octal = 00000000216

• The following example demonstrates using addition when assigning a symbol:

  $ BALANCE = BALANCE + 37 $ SHOW SYMBOL BALANCE BALANCE = 179 Hex = 000000B3 Octal = 00000000263

• The following example demonstrates using subtraction when assigning a symbol:

  $ BALANCE = BALANCE - 15416 $ SHOW SYMBOL BALANCE BALANCE = -15237 Hex = FFFFC47B Octal = 00000142173

• The following example demonstrates using a unary minus sign to change the sign of the number -142:

  $ BALANCE = -(- a142) $ SHOW SYMBOL BALANCE BALANCE = 142 Hex = 0000008E Octal = 00000000216

Table 12-2 lists different types of numeric comparisons.

In the following examples, assume that the symbol BALANCE has the value -15237 .

• In the following example, TEST_BALANCE is evaluated as 1 (True); BALANCE equals -15237 :

  $ TEST_BALANCE = BALANCE .EQ. -15237 $ SHOW SYMBOL TEST_BALANCE TEST_BALANCE = 1 ...

• In the following example, TEST_BALANCE is evaluated as 1 (True); BALANCE is greater than or equal to -15237 :

  $ TEST_BALANCE = BALANCE .GE. -15237 $ SHOW SYMBOL TEST_BALANCE TEST_BALANCE = 1 ...

• In the following example, TEST_BALANCE is evaluated as 0 (False); BALANCE is not greater than -15237 :

  $ TEST_BALANCE = BALANCE .GT. -15237 $ SHOW SYMBOL TEST_BALANCE TEST_BALANCE = 0 ...

• In the following example, TEST_BALANCE is evaluated as 1 (True); BALANCE is less than or equal to -15237 :

  $ TEST_BALANCE = BALANCE .LE. -15237 $ SHOW SYMBOL TEST_BALANCE TEST_BALANCE = 1 ...

• In the following example, TEST_BALANCE is evaluated as 0 (False); BALANCE is not less than -15237 :

  $ TEST_BALANCE = BALANCE .LT. -15237 $ SHOW SYMBOL TEST_BALANCE TEST_BALANCE = 0 ...

• In the following example, TEST_BALANCE is evaluated as 0 (False); BALANCE equals -15237 :

  $ TEST_BALANCE = BALANCE .NE. -15237 $ SHOW SYMBOL TEST_BALANCE TEST_BALANCE = 0 ...

You can perform binary (bit-level) overlays of the current symbol value by using a special format of the assignment statement. For local symbols, the format is:

For global symbols, the format is:

The elements are as follows:

To use numeric overlays, observe the following rules:

• The square brackets ([]) are required notation. No spaces are allowed between the symbol name and the left bracket.
• Literal values are assumed to be decimal.
• The maximum length for size is 32 bits.
• Replacement expression must be a numeric expression.
• When symbol-name is either undefined or defined as a string, the result of the overlay is a string. Otherwise, the result is an integer.

The following example defines the symbol BELL as the value 7. The low-order byte of BELL has the binary value 00000111. By changing the 0 at offset 5 to 1 (beginning with 0, count bits from right to left), you create the binary value 00100111 (decimal value 39):

$ BELL = 7
$ BELL[5,1] = 1
$ SHOW SYMBOL BELL
 BELL = 39   Hex = 00000027   Octal = 00000000047

The following sections describe how to use logical values and expressions.

12.8.1 Logical Operations

Some operations interpret numbers and character strings as logical data with values as follows:

• True
  A number has a logical value of true if it is odd (that is, the low-order bit is 1). A character string has a logical value of true if the first character is an uppercase or lowercase T or Y.
• False
  A number has a logical value of false if it is even (that is, the low-order bit is 0). A character string has a logical value of false if the first character is not an uppercase or lowercase T or Y.

In the following examples, DOG_COUNT is assigned the value 13. IF STATUS means if the logical value of STATUS is true.

$ STATUS = 1
$ IF STATUS THEN DOG_COUNT = 13

$ STATUS = "TRUE"
$ IF STATUS THEN DOG_COUNT = 13

A logical operation affects all the bits in the number being acted upon. The values for logical expressions are integers, and the result of the expression is an integer as well. If you specify a character string value in a logical expression, the string is converted to an integer before the expression is evaluated.

Typically, you use logical expressions to evaluate the low-order bit of a logical value; that is, to determine whether the value is true or false. You can specify the following logical operations:

• .NOT.
  The operator .NOT. reverses the bit configuration of a logical value. A true value becomes false and a false value becomes true.
• .AND.
  The operator .AND. combines two logical values as follows:

  Bit Level	Entity Level
  1 .AND. 1 = 1	true .AND. true = true
  1 .AND. 0 = 0	true .AND. false = false
  0 .AND. 1 = 0	false .AND. true = false
  0 .AND. 0 = 0	false .AND. false = false

• .OR.
  The operator .OR. combines two logical values as follows:

  Bit Level	Entity Level
  1 .OR. 1 = 1	true .OR. true = true
  1 .OR. 0 = 1	true .OR. false = true
  0 .OR. 1 = 1	false .OR. true = true
  0 .OR. 0 = 0	false .OR. false = false

The following example reverses a true value to false. The expression is evaluated as --2; the value is even and is therefore false:

$ SHOW SYMBOL STATUS
  STATUS = 1   Hex = 00000001  Octal = 00000000001
$ STATUS = .NOT. STATUS
$ SHOW SYMBOL STATUS
  STATUS = -2   Hex = FFFFFFFE  Octal = 37777777776

The following example combines a true value and a false value to produce a false value:

$ STAT1 = "TRUE"
$ STAT2 = "FALSE"
$ STATUS = STAT1 .AND. STAT2
$ SHOW SYMBOL STATUS
  STATUS = 0   Hex = 00000000  Octal = 00000000000

The following example combines a true value and a false value to produce a true value:

$ STAT1 = "TRUE"
$ STAT2 = "FALSE"
$ STATUS = STAT1 .OR. STAT2
$ SHOW SYMBOL STATUS
  STATUS = 1   Hex = 00000001  Octal = 00000000001