move exercises, lecture examples, labs into subfolders

Exercises/C10/ex4.c

@@ -0,0 +1,42 @@
+#include <stdio.h>
+
+int date_to_day(int year, int month, int day) {
+	if (month < 3) {
+		month += 12;
+		year -= 1;
+	}
+
+	return ((13*month+3)/5 + day + year + year/4 - year/100 + year/400) % 7;
+}
+
+int main() {
+	int rc, year, month, day, nd;
+
+	printf("Enter a day (yyyy-mm-dd): ");
+	rc = scanf("%d-%d-%d", &year, &month, &day);
+	if (rc != 3) {
+		printf("Failed to parse date\n");
+		return 1;
+	}
+
+	nd = date_to_day(year, month, day);
+
+	switch (nd) {
+		case 0:
+			printf("Monday\n"); break;
+		case 1:
+			printf("Tuesday\n"); break;
+		case 2:
+			printf("Wednesday\n"); break;
+		case 3:
+			printf("Thursday\n"); break;
+		case 4:
+			printf("Friday\n"); break;
+		case 5:
+			printf("Saturday\n"); break;
+		case 6:
+			printf("Sunday\n"); break;
+	}
+
+	return 0;
+}