OPEN "file.txt" FOR OUTPUT AS #1
PRINT "vvedite stroku"
INPUT a$
PRINT #1, a$
CLOSE
OPEN "file.txt" FOR INPUT AS #2
INPUT #2, a$
CLOSE
FOR i = 1 TO LEN(a$)
b$ = MID$(a$, i, 1) + b$
NEXT
OPEN "file1.txt" FOR OUTPUT AS #3
PRINT #3, b$
CLOSE
Тестирование выполнено в программе QB64 ( Скачать )