Compaq BASIC for OpenVMS
Alpha and VAX Systems
Reference Manual
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UPDATE

The UPDATE statement replaces a record in a file with a record in the record buffer. The UPDATE statement is valid on sequential, relative, and indexed files.

Format

Syntax Rules

  1. Chnl-exp is a numeric expression that specifies a channel number associated with a file. It must be immediately preceded by a number sign (#).
  2. Int-exp specifies the size of the new record.

Remarks

  1. The file associated with chnl-exp must be a disk file opened with ACCESS MODIFY.
  2. Each UPDATE statement must be preceded by a successful GET or FIND operation or BASIC signals "No current record" (ERR=131). FIND locates but does not retrieve records. Therefore, you must specify a COUNT clause when retrieving variable-length records when the preceding operation was a FIND. Int-exp must exactly match the size of the old record.
  3. If you are updating a variable-length record, and the record that you want to write out is not the same size as the record you retrieved, you must use a COUNT clause.
  4. After an UPDATE statement executes, there is no current record pointer. The next record pointer is unchanged.
  5. The length of the new record must be the same as that of the existing record for all files with fixed-length records and for all sequential files. If you specify a COUNT clause, the int-exp must match the size of the existing record.
  6. For relative files with variable-length records, the new record can be larger or smaller than the record it replaces.
  7. For indexed files with variable-length records, the new record can be larger or smaller than the record it replaces. When the program does not permit duplicate primary keys, the new record can be no longer than the size specified by the MAP or RECORDSIZE clause when the file was opened. The record must include at least the primary key field.
  8. An indexed file alternate key for the new record can differ from that of the existing record only if the OPEN statement for that file specified CHANGES for the alternate key.

Example


UPDATE #4%, COUNT 32

VAL

The VAL function converts a numeric string to a floating-point value.

Note
It is recommended that you use the DECIMAL, REAL, and INTEGER functions to convert numeric strings to numeric data types.

Format

Syntax Rules

Str-exp can contain the ASCII digits 0 to 9, uppercase E, a plus sign (+), a minus sign (-), and a period (.).

Remarks

  1. The VAL function ignores spaces and tabs.
  2. If str-exp is null, or contains only spaces and tabs, VAL returns a value of zero.
  3. The value returned by the VAL function is of the default floating-point size.

Example


DECLARE REAL real_num 
real_num = VAL("990.32") 
PRINT real_num

Output 


 990.32

VAL%

The VAL% function converts a numeric string to an integer.

Note
It is recommended that you use the DECIMAL, REAL, and INTEGER functions to convert numeric strings to numeric data types.

Format

Syntax Rules

Str-exp can contain the ASCII digits 0 to 9, a plus sign (+), or a minus sign (-).

Remarks

  1. The VAL% function ignores spaces and tabs.
  2. If str-exp is null or contains only spaces and tabs, VAL% returns a value of zero.
  3. The value returned by the VAL% function is an integer of the default size.

Example


DECLARE INTEGER ret_int 
ret_int = VAL%("789") 
PRINT ret_int

Output 


 789

VMSSTATUS

VMSSTATUS returns the underlying OpenVMS condition code when control is transferred to a BASIC error handler.

Format

Syntax Rules

None

Remarks

  1. If ERR contains the value 194, you can specify VMSSTATUS to examine the actual error that was signaled to BASIC.
  2. If an error is raised by an underlying system component such as the Run-Time Library, you can specify VMSSTATUS to determine the underlying error.
  3. If you are writing a utility routine that may be called from languages other than BASIC, you can specify VMSSTATUS in a call to LIB$SIGNAL to signal the underlying error to the caller of the utility routine.
  4. When there is no error pending, VMSSTATUS remains undefined.
  5. VMSSTATUS always returns a LONG integer.

Example


PROGRAM 
WHEN ERROR USE global_handler 
   .
   .
   .
END WHEN 
   .
   .
   .
HANDLER global_handler 
final_status% = VMSSTATUS 
END HANDLER 
END PROGRAM final_status%

WAIT

The WAIT statement specifies the number of seconds the program waits for terminal input before signaling an error.

Format

Syntax Rules

Int-exp must be from 0 to 255; if it is greater than 255, BASIC assumes a value of 255.

Remarks

  1. The WAIT statement must precede a GET operation to a terminal or an INPUT, INPUT LINE, LINPUT, MAT INPUT, or MAT LINPUT statement. Otherwise, it has no effect.
  2. Int-exp is the number of seconds BASIC waits for input before signaling the error, "Keyboard wait exhausted" (ERR=15).
  3. After BASIC executes a WAIT statement, all input statements wait the specified amount of time before BASIC signals an error.
  4. WAIT 0 disables the WAIT statement.

Example


10  DECLARE STRING your_name 
    WAIT 60 
    INPUT "You have sixty seconds to type your name";your_name 
    WAIT 0

Output 


You have sixty seconds to type your name? 
%BAS-F-KEYWAIEXH, Keyboard wait exhausted 
-BAS-I-ON_CHAFIL, on channel 0 for file SYS$INPUT:.; at user PC 00000644 
-RMS-W-TMO, timeout period expired 
-BAS-I-FROLINMOD, from line 10 in module WAIT 
%TRACE-F-TRACEBACK, symbolic stack dump follows 
module name     routine name                    line       rel PC   abs PC 
 
                                                          00007334 00007334 
----- above condition handler called with exception 001A807C: 
%BAS-F-KEYWAIEXH, keyboard wait exhausted 
-BAS-I-ON_CHAFIL, on channel 0 for file SYS$INPUT:.; at user PC 00000644 
-RMS-W-TMO, timeout period expired 
----- end of exception message 
                                                           00011618  00011618 
                                                           0000F02F  0000F02F 
                                                           0000E3F6  0000E3F6 
                                                           0001387A  0001387A 
WAIT$MAIN      WAIT$MAIN                            3      00000044  00000644

WHEN ERROR

The WHEN ERROR statement marks the beginning of a WHEN ERROR construct. The WHEN ERROR construct contains a protected region and can include an attached handler or identify a detached handler.

Format

Syntax Rules

  1. Protected-statement specifies a statement that appears within a protected region. A protected region is a special block of code that is monitored by BASIC for the occurrence of a run-time error.
  2. Handler-statement specifies the statement that appears inside an error handler.
  3. With an Attached Handler
  4. With a Detached Handler

Remarks

  1. The WHEN ERROR statement designates the start of a block of protected statements.
  2. If an error occurs inside a protected region, BASIC transfers control to the error handler associated with the WHEN ERROR statement.
  3. BASIC does not allow you to branch into a WHEN block.
  4. When BASIC encounters an END WHEN statement for an attached handler or an END HANDLER statement for a detached handler, BASIC clears the exception and transfers control to the following statement.
  5. BASIC allows you to nest WHEN blocks. If an exception occurs within a nested protected region, BASIC transfers control to the handler associated with the innermost protected region in which the error occurred.
  6. WHEN blocks cannot exist inside a handler.
  7. WHEN blocks cannot cross other block structures.
  8. You cannot specify a RESUME statement within a WHEN ERROR construct.
  9. You cannot specify an ON ERROR statement within a protected region.
  10. An attached handler must immediately follow the protected region of a WHEN ERROR IN block.
  11. Exit from a handler must occur through a RETRY, CONTINUE, or EXIT HANDLER statement, or by reaching the end of the handler delimited by END WHEN or END HANDLER.
  12. For more information about detached handlers, see the HANDLER statement.

Examples

Example 1 


!With an attached handler 
PROGRAM salary 
DECLARE REAL hourly_rate, no_of_hours, weekly_pay 
WHEN ERROR IN 
     INPUT "Enter your hourly rate";hourly_rate 
     INPUT "Enter the number of hours you worked this week";no_of_hours 
     weekly_pay = no_of_hours * hourly_rate 
     PRINT "Your pay for this week is";weekly_pay 
 
USE 
     SELECT ERR 
         CASE = 50 
               PRINT "Invalid data" 
               RETRY 
         CASE ELSE 
              EXIT HANDLER 
     END SELECT 
END WHEN 
END PROGRAM

Output 


Enter your hourly rate? 35.00 
Enter the number of hours you worked this week? 45 
Your pay for this week is 1575

Example 2 


!With a detached handler 
PROGRAM salary 
DECLARE REAL hourly_rate, no_of_hours, weekly_pay 
WHEN ERROR USE patch_work 
     INPUT "Enter your hourly rate";hourly_rate 
     INPUT "Enter the number of hours you worked this week";no_of_hours 
     weekly_pay = no_of_hours * hourly_rate 
     PRINT "Your pay for this week is";weekly_pay 
END WHEN 
 
HANDLER patch_work 
     SELECT ERR 
         CASE = 50 
               PRINT "Invalid data" 
               RETRY 
         CASE ELSE 
              EXIT HANDLER 
     END SELECT 
END HANDLER 
END PROGRAM

Output 


Enter your hourly rate?  Nineteen dollars and fifty cents 
Invalid data 
Enter your hourly rate? 19.50 
Enter the number of hours you worked this week? 40 
Your pay for this week is 780

WHILE

The WHILE statement marks the beginning of a WHILE loop or modifies the execution of another statement.

Format

Syntax Rules

A NEXT statement must end the WHILE loop.

Remarks

  1. Conditional
    BASIC evaluates cond-exp before each loop iteration. If the expression is true (value nonzero), BASIC executes the loop. If the expression is false (value zero), control passes to the first executable statement after the NEXT statement.
  2. Statement Modifier
    BASIC executes the statement repeatedly as long as cond-exp is true.

Examples

Example 1 


!Conditional 
WHILE X < 100 
    X = X + SQR(X) 
NEXT

Example 2 


!Statement Modifier 
X% = X% + 1% WHILE X% < 100%

XLATE$

The XLATE$ function translates one string to another by referencing a table string you supply.

Format

Syntax Rules

  1. Str-exp1 is the input string.
  2. Str-exp2 is the table string.

Remarks

  1. Str-exp2 can contain up to 256 ASCII characters, numbered from 0 to 255; the position of each character in the string corresponds to an ASCII value. Because 0 is a valid ASCII value (null), the first position in the table string is position zero.
  2. XLATE$ scans str-exp1 character by character, from left to right. It finds the ASCII value n of the first character in str-exp1 and extracts the character it finds at position n in str-exp2. XLATE$ then appends the character from str-exp2 to str-var. XLATE$ continues this process, character by character, until the end of str-exp1 is reached.
  3. The output string may be smaller than the input string for the following reasons:

Example


DECLARE STRING A, table, source 
A = "abcdefghijklmnopqrstuvwxyz" 
table = STRING$(65, 0) + A 
LINPUT " Type a string of uppercase letters"; source 
PRINT XLATE$(source, table)

Output 


Type a string of uppercase letters? ABCDEFG 
abcdefg

Appendix A
ASCII Character Codes

ASCII is a 7-bit character code with an optional parity bit (8) added for many devices. Programs normally use seven bits internally with the eighth bit being zero; the extra bit is either stripped (on input) or added by a device driver (on output) so the program will operate with either parity- or nonparity-generating devices. The eighth bit is reserved for future standardization.

The International Reference Version (IRV) of ISO Standard 646 is identical to the IRV in CCITT Recommendation V.3 (International alphabet No. 5). The character sets are the same as ASCII except that the ASCII dollar sign (hexadecimal 24) is the international currency sign (###).

ISO Standard 646 and CCITT V.3 also specify the structure for national character sets, of which ASCII is the U.S. national set. Certain specific characters are reserved for national use. Table A-1 contains the values and symbols.

Table A-1 ASCII Characters Reserved for National Use
Hexadecimal Value IRV ASCII
23 # #
24 ### $ (General currency symbol vs. dollar sign)
40 @ @
5B [ [
5C \ \
5D ] ]
5E ^ ^
60 ` `
7B { {
7C | |
7D } }
7E ~ Tilde

ISO Standard 646 and CCITT Recommendation V.3 (International Alphabet No. 5) are identical to ASCII except that the number sign (23) is represented as ## instead of #, and certain characters are reserved for national use. Table A-2 list the ASCII codes.

Table A-2 ASCII Codes
Decimal
Code 		8-Bit
Hexadecimal
Code 		Character Remarks
0 00 NUL Null (tape feed)
1 01 SOH Start of heading (^A)
2 02 STX Start of text (end of address, ^B)
3 03 ETX End of text (^C)
4 04 EOT End of transmission (shuts off the TWX machine ^D)
5 05 ENQ Enquiry (WRU, ^E)
6 06 ACK Acknowledge (RU, ^F)
7 07 BEL Bell (^G)
8 08 BS Backspace (^H)
9 09 HT Horizontal tabulation (^I)
10 0A LF Line feed (^J)
11 0B VT Vertical tabulation (^K)
12 0C FF Form feed (page, ^L)
13 0D CR Carriage return (^M)
14 0E SO Shift out (^N)
15 0F SI Shift in (^O)
16 10 DLE Data link escape (^P)
17 11 DC1 Device control 1 (^Q)
18 12 DC2 Device control 2 (^R)
19 13 DC3 Device control 3 (^S)
20 14 DC4 Device control 4 (^T)
21 15 NAK Negative acknowledge (ERR, ^U)
22 16 SYN Synchronous idle (^V)
23 17 ETB End-of-transmission block (^W)
24 18 CAN Cancel (^X)
25 19 EM End of medium (^Y)
26 1A SUB Substitute (^Z)
27 1B ESC Escape (prefix of escape sequence)
28 1C FS File separator
29 1D GS Group separator
30 1E RS Record separator
31 1F US Unit separator
32 20 SP Space
33 21 ! Exclamation point
34 22 " Double quotation mark
35 23 # Number sign
36 24 $ Dollar sign
37 25 % Percent sign
38 26 & Ampersand
39 27 ' Apostrophe
40 28 ( Left (open) parenthesis
41 29 ) Right (close) parenthesis
42 2A * Asterisk
43 2B + Plus sign
44 2C , Comma
45 2D -- Minus sign, hyphen
46 2E . Period (decimal point)
47 2F / Slash (slant)
48 30 0 Zero
49 31 1 One
50 32 2 Two
51 33 3 Three
52 34 4 Four
53 35 5 Five
54 36 6 Six
55 37 7 Seven
56 38 8 Eight
57 39 9 Nine
58 3A : Colon
59 3B ; Semicolon
60 3C < Less than (left angle bracket)
61 3D = Equal sign
62 3E > Greater than (right angle bracket)
63 3F ? Question mark
64 40 @ Commercial at
65 41 A Uppercase A
66 42 B Uppercase B
67 43 C Uppercase C
68 44 D Uppercase D
69 45 E Uppercase E
70 46 F Uppercase F
71 47 G Uppercase G
72 48 H Uppercase H
73 49 I Uppercase I
74 4A J Uppercase J
75 4B K Uppercase K
76 4C L Uppercase L
77 4D M Uppercase M
78 4E N Uppercase N
79 4F O Uppercase O
80 50 P Uppercase P
81 51 Q Uppercase Q
82 52 R Uppercase R
83 53 S Uppercase S
84 54 T Uppercase T
85 55 U Uppercase U
86 56 V Uppercase V
87 57 W Uppercase W
88 58 X Uppercase X
89 59 Y Uppercase Y
90 5A Z Uppercase Z
91 5B [ Left square bracket
92 5C \ Backslash (reverse slant)
93 5D ] Right square bracket
94 5E ^ Circumflex (caret)
95 5F _ Underscore (underline)
96 60 ` Grave accent
97 61 a Lowercase a
98 62 b Lowercase b
99 63 c Lowercase c
100 64 d Lowercase d
101 65 e Lowercase e
102 66 f Lowercase f
103 67 g Lowercase g
104 68 h Lowercase h
105 69 i Lowercase i
106 6A j Lowercase j
107 6B k Lowercase k
108 6C l Lowercase l
109 6D m Lowercase m
110 6E n Lowercase n
111 6F o Lowercase o
112 70 p Lowercase p
113 71 q Lowercase q
114 72 r Lowercase r
115 73 s Lowercase s
116 74 t Lowercase t
117 75 u Lowercase u
118 76 v Lowercase v
119 77 w Lowercase w
120 78 x Lowercase x
121 79 y Lowercase y
122 7A z Lowercase z
123 7B { Left brace
124 7C | Vertical line
125 7D } Right brace
126 7E ~ Tilde
127 7F DEL Delete (rubout)

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