play with structs and pointers

ch6/main.c

@@ -0,0 +1,29 @@
+#include <stdio.h>
+
+typedef int Length;
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))
+
+void test() {
+  // struct point p1; // COMPILER ERROR: unknown storage size because struct not declared in this scope
+  struct point *p1; // works because it's a forward declaration for an opaque pointer, and incomplete type, but cannot do pointer arithmetic
+
+  printf("struct pointer size: %d\n", sizeof(struct point *));
+  printf("int * size: %d\n", sizeof(int *));
+  printf("char * size: %d\n", sizeof(char *));
+}
+
+int main(int argc, char *argv[]) {
+  // you can declare the struct template along with a declaration and definition of a variable,
+  // and then you can still reuse the struct template again later, however, probably not in another function or file scope
+  struct point {
+    int x;
+    int y;
+  } p = {100, 100};
+
+  struct point another_point = {0, 3};
+
+  printf("struct size: %d\n", sizeof(struct point));
+
+  test();
+}