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Task/Caesar-cipher/FreeBASIC/caesar-cipher.freebasic

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+' FB 1.05.0 Win64
+
+Sub Encrypt(s As String, key As Integer)
+  Dim c As Integer
+  For i As Integer = 0 To Len(s)
+    Select Case As Const s[i]
+      Case 65 To 90
+        c = s[i] + key
+        If c > 90 Then c -= 26
+        s[i] = c
+      Case 97 To 122
+        c = s[i] + key
+        If c > 122 Then c -= 26
+        s[i] = c
+    End Select
+  Next
+End Sub
+
+Sub Decrypt(s As String, key As Integer)
+  Dim c As Integer
+  For i As Integer = 0 To Len(s)
+    Select Case As Const s[i]
+      Case 65 To 90
+        c = s[i] - key
+        If c < 65 Then c += 26
+        s[i] = c
+      Case 97 To 122
+        c = s[i] - key
+        If c < 97 Then c += 26
+        s[i] = c
+    End Select
+  Next
+End Sub
+
+Dim As String s = "Bright vixens jump; dozy fowl quack."
+Print "Plain text : "; s
+Encrypt s, 8
+Print "Encrypted  : "; s
+Decrypt s, 8
+Print "Decrypted  : "; s
+Sleep