added chapter 20, 21 and 22

0x0014_static-variables/main.c

@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include "pico/stdlib.h"
+#include "pico/cyw43_arch.h"
+
+int main(void)
+{
+    stdio_init_all();
+
+    while (true)
+    {
+        static int static_fav_num = 42;
+        int regular_fav_num = 42;
+
+        printf("static_fav_num: %d\r\n", static_fav_num);
+        printf("regular_fav_num: %d\r\n", regular_fav_num);
+
+        static_fav_num++;
+        regular_fav_num++;
+    }
+}