Data commit

Task/Caesar-cipher/C/caesar-cipher.c

@@ -0,0 +1,52 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+
+#define caesar(x) rot(13, x)
+#define decaesar(x) rot(13, x)
+#define decrypt_rot(x, y) rot((26-x), y)
+
+void rot(int c, char *str)
+{
+	int l = strlen(str);
+
+        const char*  alpha_low  = "abcdefghijklmnopqrstuvwxyz";
+
+        const char*  alpha_high = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+
+       char subst;  /* substitution character */
+       int idx;    /* index */
+
+         int i; /* loop var */
+
+	for (i = 0; i < l; i++)  /* for each letter in string */
+	{
+		if( 0 == isalpha(str[i]) )  continue; /* not alphabet character */
+
+                idx = (int) (tolower(str[i]) - 'a') + c) % 26; /* compute index */
+
+		if( isupper(str[i]) )
+                    subst = alpha_high[idx];
+                else
+                    subst = alpha_low[idx];
+
+               str[i] = subst;
+
+	}
+}
+
+
+int main(int argc, char** argv)
+{
+	char str[] = "This is a top secret text message!";
+	
+	printf("Original: %s\n", str);
+	caesar(str);
+	printf("Encrypted: %s\n", str);
+	decaesar(str);
+	printf("Decrypted: %s\n", str);
+	
+	return 0;
+}