HP OpenVMS Systems Documentation

HP BASIC for OpenVMS
Reference Manual

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, HP BASIC assumes a value of 255.

Remarks

• 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.
• Int-exp is the number of seconds HP BASIC waits for input before signaling the error "Keyboard wait exhausted" (ERR=15).
• After HP BASIC executes a WAIT statement, all input statements wait the specified amount of time before HP BASIC signals an error.
• 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

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

With an Attached Handler
WHEN ERROR IN

protected-statement

[ protected-statement,... ]

USE

handler-statement

[ handler-statement,... ]

END WHEN

With a Detached Handler
WHEN ERROR USE handler-name

protected-statement

[ protected-statement,... ]

END WHEN

HANDLER handler-name

[ handler-statement,... ]

END HANDLER

Syntax Rules

• Protected-statement specifies a statement that appears within a protected region. A protected region is a special block of code that is monitored by HP BASIC for the occurrence of a run-time error.
• Handler-statement specifies the statement that appears inside an error handler.
• With an Attached Handler
  • The keyword USE marks the start of handler statements.
  • An attached handler must be delimited by a USE and END WHEN statement.
• With a Detached Handler
  • The keyword USE names the associated handler for the protected region.
  • Handler-name must be a valid HP BASIC identifier and cannot be the same as any label, DEF, DEF*, SUB, FUNCTION, or PICTURE name within the same program unit.
  • A detached handler must be delimited by a HANDLER and END HANDLER statement.
  • You can specify the same detached handler with more than one WHEN ERROR USE statement.

Remarks

• The WHEN ERROR statement designates the start of a block of protected statements.
• If an error occurs inside a protected region, HP BASIC transfers control to the error handler associated with the WHEN ERROR statement.
• HP BASIC does not allow you to branch into a WHEN block.
• When HP BASIC encounters an END WHEN statement for an attached handler or an END HANDLER statement for a detached handler, HP BASIC clears the exception and transfers control to the following statement.
• HP BASIC allows you to nest WHEN blocks. If an exception occurs within a nested protected region, HP BASIC transfers control to the handler associated with the innermost protected region in which the error occurred.
• WHEN blocks cannot exist inside a handler.
• WHEN blocks cannot cross other block structures.
• You cannot specify a RESUME statement within a WHEN ERROR construct.
• You cannot specify an ON ERROR statement within a protected region.
• An attached handler must immediately follow the protected region of a WHEN ERROR IN block.
• 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.
• 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

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

Format

Conditional
WHILE cond-exp

[ statement ]...
.
.
. NEXT

Statement Modifier
statement WHILE cond-exp

Syntax Rules

A NEXT statement must end the WHILE loop.

Remarks

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

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

Format

Syntax Rules

• Str-exp1 is the input string.
• Str-exp2 is the table string.

Remarks

• 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.
• 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.
• The output string may be smaller than the input string for the following reasons:
  • XLATE$ does not translate nulls. If the character at position n in str-exp2 is a null, XLATE$ does not append that character to str-var.
  • If the ASCII value of the input character is outside the range of positions in str-exp2, XLATE$ does not append any character to str-var.

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

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.

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.