42 lines
1.2 KiB
Racket
42 lines
1.2 KiB
Racket
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#lang racket
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(define memory (make-vector 1024 #\nul))
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(define flag (if (getenv "FLAG") (getenv "FLAG") "NO-FLAG-DEFINED"))
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(define (write-to-memory! str memory-start-index)
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(define str-length (string-length str))
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(define (loop str-index)
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(when (< str-index str-length)
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(vector-set! memory (+ memory-start-index str-index) (string-ref str str-index))
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(loop (+ str-index 1))))
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(loop 0))
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(define (init-memory!)
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(write-to-memory! "admin\0" 8)
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(write-to-memory! (string-append flag "\0") 14))
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(init-memory!)
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(define (read-from-memory memory-start-index)
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(define (loop str curr-index)
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(if (equal? (vector-ref memory curr-index) #\nul)
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str
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(loop (string-append str (string (vector-ref memory curr-index))) (+ curr-index 1))))
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(loop "" memory-start-index))
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(define (main)
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(display "Editing user name 'admin'\n")
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(display "Enter new name: ")
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(define new-username (symbol->string (read)))
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(if (> (string-length new-username) (- 14 8))
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(begin
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(display "Error: new username cannot be longer than old username\n")
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(main))
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(begin
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(write-to-memory! new-username 8)
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(display (string-append "Successfully changed username of 'admin' to '" (read-from-memory 8) "'")))))
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(main)
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