1. User-defined data types
Structures
A collection of other data types
Used a lot for organized complex data structures
Can be used for Object-Orient Programming in C
Unions
A combination of various different types

2. Basic Structures -- Declaration
struct [tag] {members} [variables] ;
Type declaration with tag:
struct point {
int x;
int y; };
Used later for variable declaration:
struct point a, b;
Also valid:
int y; } a, b;
struct { int x; int y; } a, b;

3. Structure Usage Member access Hierarchical struct sname.member;
a.x and a.y;
Hierarchical struct
struct members can be of any type, including a struct
nested structs
struct rect {
struct point low_left;
struct point top_right;
} box;
box.low_left.x;

4. Structure Arithmetic member access initiation, copy/assignment
a.x = 2;
a.y = 1;
initiation, copy/assignment
struct point b = {1, 2};
b = a;
b = {1,2}; /* Wrong */
Need to be of the same type

5. Structure and Functions
Use function to initialize structure variables
make_point(1, 2);
More structure functions
make_rect (a, b);
distance (a, b);
All variables are passed by value, can be inefficient for large structures
structure functions w/ pointers
distance (&a, &b);
Member access with structure pointers
sname_pt->member
(*sname_pt).member

6. Structure Arrays A new declaration of rectangle
struct point {int x, int y} pt[2];
Students in class c459.21
struct student {
char name[10];
int score; };
struct student c459[10];

7. Structure Arrays -- Continued
Calculate average score
int average(struct student c1[], int n) {
int i, total =0;
for (i = 0; i < n ; i++) {
total += c1[i].score; }
return (total/(double)n);
int main() {
struct student c459[] = {
“John”, 90,
“Adam”, 80, };
average(c459,
sizeof(c459)/sizeof(struct student));
return 0; }

8. Structure Pointers Calculate average score int main()
int average(struct student *p, int n) {
int i, total =0;
for (i = 0; i < n ; p++, i++) {
total += p->score; }
return (total/(double)n);
int main() {
struct student c459[] = {
“John”, 90,
“Adam”, 80, };
average(c459,
sizeof(c459)/sizeof(struct student));
return 0; }

9. Unions A combination of various different types
Syntax like structures, but different implications
The size of a union is the maxim of all
The size of a struct is at least the combination of all
Same memory content with different representation
union num_rep {
int x;
short s;
char c; };
union addr {
char *cp;
int *ip;
int value; };

10. More on user defined data types
sizeof
Safe way to tell the size of structures or unions
struct s2 {
int x;
char c;
short s; };
typedef
Specify a new name for the same type