INPUT


The INPUT statement allows the program to collect data from the current input device, which will normally be the terminal keyboard but may be stacked input from the same or separate program.

 

COMMAND SYNTAX

INPUT {@(expression1{, expression2 )}{:} Var{{, expression3}, expression4} {:}{_} {WITH expression5} {FOR expression6 THEN|ELSE statements}

 

SYNTAX ELEMENTS

@(expression1, expression2) allows the screen cursor to be positioned to the specified column and row before the input prompt is sent to the screen. The syntax for this is exactly the same as for the @( ) function described earlier.

Var is the variable in which the input data is to be stored.

expression3, when specified, should evaluate to a numeric value. This will cause input to be terminated with an automatic newline sequence after exactly this number of characters has been input. If the _ option is specified with expression4 then the automatic newline sequence is not specified but any subsequent input characters are belled to the terminal and thrown away.

expression4, when specified, should evaluate to a sequence of 1 to 3 characters. The first character will be printed expression3 times to define the field on the terminal screen. At the end of the input if less than expression3 characters were input then the rest of the field is padded with the second character if it was supplied. If the third character is supplied then the cursor will be positioned after the last character input rather than at the end of the input field.

The : option, when specified, suppress the echoing of the newline sequence to the terminal. This will leave the cursor positioned after the last input character on the terminal screen.

WITH expression5 allows the default input delimiter (the newline sequence) to be changed. When specified, expression5, should evaluate to a string of up to 256 characters, each of which may delimit the input field. If this clause is used then the newline sequence is removed as a delimiter and must be specified explicitly within expression5 as CHAR(10).

The FOR clause allows the INPUT statement to time out after a specified waiting period instead of blocking as normal. Expression6 should evaluate to a numeric value, which will be taken as the number of deci-seconds (tenths of a second) to wait before timing out. The time-out value is used as the time between each keystroke and should a time-out occur, Var will hold the characters that were input until the time-out.

The FOR clause requires either or both of the THEN and ELSE clauses. If no time-out occurs the THEN clause is taken. If a time-out does occur the ELSE clause is taken.

 

NOTES

The INPUT statement will always examine the data input stack before requesting data from the input device. If data is present on the stack then it is used to satisfy INPUT statements one field at a time until the stack is exhausted. Once exhausted, the INPUT statement will revert to the input device for further input. There is no way (by default) to input a null field to the [email protected] statement. If the [email protected] statement receives the newline sequence only as input, then the Var will be unchanged. The INPUTNULL statement should be used to define a character that indicates a NULL input.

The CONTROL-CHARS command can be used to control whether or not control characters (i.e. those outside the range x'1F' - x'7F') are accepted by INPUT.

See also IN, INPUTNULL.

EXAMPLES

Answer = "
LOOP
WHILE Answer = " DO
    INPUT Answer,1 FOR 10 ELSE
        GOSUB UpdateClock
    END
REPEAT

The above example attempts to read a single character from the input device for 10 deci-seconds (1 second). The LOOP will exit when a character has been input otherwise every second it will call the local subroutine UpdateClock.


jBC