Talk:Substitution cipher: Difference between revisions

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 This task should really specify some examples to be tried by each implementation. --[[User:Rdm|Rdm]] ([[User talk:Rdm|talk]]) 14:32, 15 October 2015 (UTC)
+== Task: substitute cipher in PowerBASIC ==
+'PBCC 6.03 version
+' uses same alphabet and key as Ada language example
+$string1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+$string2 = "VsciBjedgrzyHalvXZKtUPumGfIwJxqOCFRApnDhQWobLkESYMTN"
+%true = -1
+%false = 0
+FUNCTION PBMAIN() AS LONG
+  PROCESS1 "plain.txt", "encrypted.txt", %true
+  PROCESS1 "encrypted.txt", "decrypted.txt",%false
+  PRINT
+  PRINT "Press any key to quit"
+  WAITKEY$
+END FUNCTION
+SUB process1(inputFile AS STRING, outputFile AS STRING, encrypt AS INTEGER)
+  DIM i AS INTEGER
+  OPEN inputFile FOR INPUT AS #1
+  IF ERR > 0 THEN
+    PRINT "Unable to open input file"
+    WAITKEY$
+    END
+  END IF
+  DIM alpha AS STRING, key1 AS STRING
+  IF encrypt THEN
+    alpha = $string1 : key1 = $string2
+  ELSE
+    alpha = $string2 : key1 = $string1
+  END IF
+  OPEN outputFile FOR OUTPUT AS #2
+  DIM s AS STRING
+  DIM p AS INTEGER
+  DIM currentChar AS INTEGER
+  WHILE NOT EOF(1)
+    LINE INPUT #1, s
+    FOR i = 1 TO LEN(s)
+      currentChar = ASC(MID$(s, i, 1))
+      IF (currentChar >= 65 AND currentChar <= 90) OR (currentChar >= 97 AND currentChar <= 122) THEN
+        p = INSTR(alpha, MID$(s, i, 1))
+        MID$(s, i, 1) = MID$(key1, p, 1)
+      END IF
+    NEXT
+    PRINT #2, s
+  WEND
+  CLOSE #1 : CLOSE #2
+END SUB