Data commit

Task/Caesar-cipher/Modula-2/caesar-cipher.mod2

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+MODULE CaesarCipher;
+FROM Conversions IMPORT IntToStr;
+FROM Terminal IMPORT WriteString, WriteLn, ReadChar;
+
+TYPE String = ARRAY[0..64] OF CHAR;
+
+PROCEDURE Encrypt(p : String; key : CARDINAL) : String;
+VAR e : String;
+VAR i,t : CARDINAL;
+VAR c : CHAR;
+BEGIN
+    FOR i:=0 TO HIGH(p) DO
+        IF p[i]=0C THEN BREAK; END;
+
+        t := ORD(p[i]);
+        IF (p[i]>='A') AND (p[i]<='Z') THEN
+            t := t + key;
+            IF t>ORD('Z') THEN
+                t := t - 26;
+            END;
+        ELSIF (p[i]>='a') AND (p[i]<='z') THEN
+            t := t + key;
+            IF t>ORD('z') THEN
+                t := t - 26;
+            END;
+        END;
+        e[i] := CHR(t);
+    END;
+    RETURN e;
+END Encrypt;
+
+PROCEDURE Decrypt(p : String; key : CARDINAL) : String;
+VAR e : String;
+VAR i,t : CARDINAL;
+VAR c : CHAR;
+BEGIN
+    FOR i:=0 TO HIGH(p) DO
+        IF p[i]=0C THEN BREAK; END;
+
+        t := ORD(p[i]);
+        IF (p[i]>='A') AND (p[i]<='Z') THEN
+            t := t - key;
+            IF t<ORD('A') THEN
+                t := t + 26;
+            END;
+        ELSIF (p[i]>='a') AND (p[i]<='z') THEN
+            t := t - key;
+            IF t<ORD('a') THEN
+                t := t + 26;
+            END;
+        END;
+        e[i] := CHR(t);
+    END;
+    RETURN e;
+END Decrypt;
+
+VAR txt,enc : String;
+VAR key : CARDINAL;
+BEGIN
+    txt := "The five boxing wizards jump quickly";
+    key := 3;
+
+    WriteString("Original:  ");
+    WriteString(txt);
+    WriteLn;
+
+    enc := Encrypt(txt, key);
+    WriteString("Encrypted: ");
+    WriteString(enc);
+    WriteLn;
+
+    WriteString("Decrypted: ");
+    WriteString(Decrypt(enc, key));
+    WriteLn;
+
+    ReadChar;
+END CaesarCipher.