From dd75cd75e74217ba004af546bae987086cac2212 Mon Sep 17 00:00:00 2001
From: Alvie Rahman <alvierahman90@gmail.com>
Date: Thu, 26 Oct 2023 20:24:04 +0100
Subject: [PATCH] complete c21

---
 Exercises/C21/ex1.c | 20 ++++++++++++++++++++
 Exercises/C21/ex2.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 Exercises/C21/ex1.c
 create mode 100644 Exercises/C21/ex2.c

diff --git a/Exercises/C21/ex1.c b/Exercises/C21/ex1.c
new file mode 100644
index 0000000..b64fe16
--- /dev/null
+++ b/Exercises/C21/ex1.c
@@ -0,0 +1,20 @@
+#include <stdlib.h>
+#include <stdio.h>
+
+int main(int argc, char *argv[]) {
+	int age;
+	char name[10];
+
+	if ( argc != 3 )
+	{
+		printf ("USAGE: %s name age\n",argv[0]);
+		exit (0);
+	} 
+
+	sscanf(argv[1],"%s",name);
+	sscanf(argv[2],"%d",&age);
+
+	printf ("age=%d name=%s\n", age, name);
+
+	return 0;
+}
diff --git a/Exercises/C21/ex2.c b/Exercises/C21/ex2.c
new file mode 100644
index 0000000..3aa50ba
--- /dev/null
+++ b/Exercises/C21/ex2.c
@@ -0,0 +1,44 @@
+// Modified from C10 Ex5
+
+#include <stdlib.h>
+#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;
+}
+
+void print_day_of_week(int day) {
+	switch (day) {
+		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;
+	}
+}
+
+int main(int argc, char *argv[]) {
+	int rc, year, month, day, nd;
+
+	if ( argc != 4 )
+	{
+		printf ("USAGE: %s year month day\n",argv[0]);
+		exit (0);
+	} 
+
+	sscanf(argv[1],"%d",&year);
+	sscanf(argv[2],"%d",&month);
+	sscanf(argv[3],"%d",&day);
+
+	nd = date_to_day(year, month, day);
+	print_day_of_week(nd);
+
+	return 0;
+}