Data commit

Task/Substitution-cipher/FreeBASIC/substitution-cipher.basic

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+' FB 1.05.0 Win64
+
+' uses same alphabet and key as Ada language example
+Const string1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+Const string2 = "VsciBjedgrzyHalvXZKtUPumGfIwJxqOCFRApnDhQWobLkESYMTN"
+
+Sub process(inputFile As String, outputFile As String, encrypt As Boolean)
+   Open inputFile For Input As #1
+   If err > 0 Then
+     Print "Unable to open input file"
+     Sleep
+     End
+   End If
+   Dim As String alpha, key
+   If encrypt Then
+     alpha = string1 : key = string2
+   Else
+     alpha = string2 : key = string1
+   End If
+   Open outputFile For Output As #2
+   Dim s As String
+   Dim p As Integer
+   While Not Eof(1)
+     Line Input #1, s
+     For i As Integer = 0 To Len(s) - 1
+       If (s[i] >= 65 AndAlso s[i] <= 90) OrElse (s[i] >= 97 AndAlso s[i] <= 122) Then
+         p =  Instr(alpha, Mid(s, i + 1, 1)) - 1
+         s[i] = key[p]
+       End If
+     Next
+     Print #2, s
+   Wend
+   Close #1 : Close #2
+End Sub
+
+process "plain.txt", "encrypted.txt", true
+process "encrypted.txt", "decrypted.txt", false
+Print
+Print "Press any key to quit"
+Sleep