Execute Brain****/BASIC/QuickBasic
This implementation is very limited by BASIC. The memory space cannot be resized (not Turing complete). It is initially set to 20000, but can be changed before running the program. Input will not accept return characters at all. A buffer is programmed in for input, as well.
The program first asks for a filename for BF source code. If no filename is given (return hit without typing anything), the program accepts source from std in. The program then cleans up the code similarly to how RCBF (Java) does and reports an uneven bracket error if it exists. Input works with a programmed buffer. It takes in an entire line if the buffer is empty, or it takes the first character from the buffer if it's not (just like the way you'd expect a buffer to work). Looping works the same as in RCBF (Java), as well.
<qbasic>CLS memsize = 20000 instChars$ = "[]<>.,+-" 'valid characters ptr = 0 'memory pointer
INPUT "Filename (blank to use std in)...? ", filename$ IF filename$ = "" THEN
DO
LINE INPUT line$
source$ = source$ + line$
LOOP WHILE line$ <> ""
ELSE
OPEN filename$ FOR INPUT AS #1
DO
LINE INPUT #1, line$
source$ = source$ + line$
LOOP UNTIL EOF(1)
END IF CLOSE 'close the file if it's open
'let's clean the code up bktCnt = 0 FOR i = 1 TO LEN(source$)
char$ = MID$(source$, i, 1)
in = 0
'check to see if this is a valid instruction character
FOR j = 1 TO LEN(instChars$)
IF char$ = MID$(instChars$, j, 1) THEN
'valid instruction characters kept, others ignored
in = 1
EXIT FOR
END IF
NEXT j
IF in THEN
code$ = code$ + char$
'count brackets
IF char$ = "[" THEN bktCnt = bktCnt + 1
IF char$ = "]" THEN bktCnt = bktCnt - 1
END IF
NEXT i
IF bktCnt THEN 'mismatched brackets
PRINT "Uneven brackets"
END
END IF
DIM SHARED memory(0 TO memsize) AS INTEGER 'fixed-size memory space :( inLine$ = "" 'input buffer FOR i = 1 TO LEN(code$) 'loop through the code
DIM inChar AS STRING * 1 'single character for input
instruction$ = MID$(code$, i, 1) 'get the instruction we're on
SELECT CASE instruction$
CASE "+"
memory(ptr) = memory(ptr) + 1
CASE "-"
memory(ptr) = memory(ptr) - 1
CASE "."
PRINT CHR$(memory(ptr));
CASE ","
IF inLine$ = "" THEN LINE INPUT inLine$ 'buffer input
inChar = LEFT$(inLine$, 1) 'take the first char off the buffer
inLine$ = MID$(inLine$, 2) 'delete it from the buffer
memory(ptr) = ASC(inChar) 'use it
CASE ">"
ptr = ptr + 1
IF ptr > 20000 THEN
PRINT "Memory pointer out of range"
END
END IF
CASE "<"
ptr = ptr - 1
IF ptr < 0 THEN
PRINT "Memory pointer out of range"
END
END IF
CASE "["
IF memory(ptr) = 0 THEN
bktCnt = 1'count the bracket we're on
i = i + 1'move the code pointer to the next char
WHILE bktCnt <> 0
'count nested loops till we find the matching one
IF MID$(code$, i, 1) = "]" THEN bktCnt = bktCnt - 1
IF MID$(code$, i, 1) = "[" THEN bktCnt = bktCnt + 1
i = i + 1 'search forward
WEND
END IF
CASE "]"
IF memory(ptr) <> 0 THEN
bktCnt = -1'count the bracker we're on
i = i - 1'move the code pointer back a char
WHILE bktCnt <> 0
'count nested loops till we fine the matching one
IF MID$(code$, i, 1) = "]" THEN bktCnt = bktCnt - 1
IF MID$(code$, i, 1) = "[" THEN bktCnt = bktCnt + 1
i = i - 1 'search backwards
WEND
END IF
END SELECT
NEXT i</qbasic>