Data commit

Task/Rot-13/C/rot-13.c

@@ -0,0 +1,51 @@
+#include <ctype.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static char rot13_table[UCHAR_MAX + 1];
+
+static void init_rot13_table(void) {
+	static const unsigned char upper[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+	static const unsigned char lower[] = "abcdefghijklmnopqrstuvwxyz";
+
+	for (int ch = '\0'; ch <= UCHAR_MAX; ch++) {
+		rot13_table[ch] = ch;
+	}
+	for (const unsigned char *p = upper; p[13] != '\0'; p++) {
+		rot13_table[p[0]] = p[13];
+		rot13_table[p[13]] = p[0];
+	}
+	for (const unsigned char *p = lower; p[13] != '\0'; p++) {
+		rot13_table[p[0]] = p[13];
+		rot13_table[p[13]] = p[0];
+	}
+}
+
+static void rot13_file(FILE *fp)
+{
+	int ch;
+	while ((ch = fgetc(fp)) != EOF) {
+		fputc(rot13_table[ch], stdout);
+	}
+}
+
+int main(int argc, char *argv[])
+{
+	init_rot13_table();
+
+	if (argc > 1) {
+		for (int i = 1; i < argc; i++) {
+			FILE *fp = fopen(argv[i], "r");
+			if (fp == NULL) {
+				perror(argv[i]);
+				return EXIT_FAILURE;
+			}
+			rot13_file(fp);
+			fclose(fp);
+		}
+	} else {
+		rot13_file(stdin);
+	}
+	return EXIT_SUCCESS;
+}