Data update

Task/Caesar-cipher/SheerPower-4GL/caesar-cipher.4gl

@@ -0,0 +1,46 @@
+declare string plaintext$, ciphertext$, decrypted$
+
+plaintext$  = 'The Quick Brown Fox Jumps Over The Lazy Dog'
+
+print 'Plaintext:  '; plaintext$
+
+ciphertext$ = caesar$(plaintext$, 13)
+print 'ROT13:      '; ciphertext$
+
+decrypted$  = caesar$(ciphertext$, 13)
+print 'Decrypted:  '; decrypted$
+
+print
+print 'Shift 3 example (classic Caesar):'
+ciphertext$ = caesar$('Attack at dawn', 3)
+print 'Encrypted:  '; ciphertext$
+print 'Decrypted:  '; caesar$(ciphertext$, 23)
+
+! =============================================================================
+! Routine: caesar$(text$, shift%)
+!
+! Shift each letter in text$ by shift% positions.  A–Z and a–z wrap
+! within their own ranges; all other characters are copied unchanged.
+! =============================================================================
+routine caesar$(text$, shift%)
+  declare string result$, ch$
+  declare integer i%, code%
+
+  result$ = ''
+  for i% = 1 to len(text$)
+    ch$   = mid$(text$, i%, 1)
+    code% = ord(ch$)
+
+    if code% >= 65 and code% <= 90 then
+      ! Uppercase A–Z: rotate within 65–90
+      result$ = result$ + chr$((code% - 65 + shift%) mod 26 + 65)
+    elseif code% >= 97 and code% <= 122 then
+      ! Lowercase a–z: rotate within 97–122
+      result$ = result$ + chr$((code% - 97 + shift%) mod 26 + 97)
+    else
+      ! Non-letter: pass through unchanged
+      result$ = result$ + ch$
+    end if
+  next i%
+  caesar$ = result$
+end routine