1. Array of Structures A structure holds only one record But a record
can contain many
fields
To deal with a collection of records, use an
Array of structures
How?
/* define a struct */
typedef struct{int x,y;} point;
...
/* in a function,
declare an array of structs */
point polygon_point[10];
142 T -1

2. How to access the fields of a struct in
an array of structs?
combine what we know about structs
and arrays
polygon_point[6].x
is the x coordinate of the 7th point of the
polygon
In the memory
an int x y
a struct
polygon_point[0]
polygon_point[1]
polygon_point is a pointer of type pointer
to a struct point (point *)
142 T -2

3. Pointers and arrays of structs
polygon_point is the name of an array
Array expression
Pointer expression
polygon_point[2]
*(polygon_point+2)
polygon_point[2].x
(*(polygon_point+2)).x
parentheses are
important! or
(polygon_point+2)->x
142 T -3

4. Using arrays of structs
Drawing the polygon:
int main(void) {
...
GP142_point polygon[5];
for(i=0; i<4; i++)
/*Connect point i to point i+1*/
GP142_lineP(BLACK,polygon[i],
polygon[i+1],0);
/*Connect point 4 to point 0*/
GP142_lineP(BLACK,polygon[4],
polygon[5],0); }
142 T - 4

5. void draw_poly(GP142_point polygon[5]) int i;
Or with a function
int main(void) {
...
GP142_point polygon[5];
/* draw the polygon */
draw_poly(polygon) }
void draw_poly(GP142_point polygon[5])
int i;
/*Connect point i to point i+1*/
GP142_lineP(BLACK,polygon[i],
polygon[i+1],0);
/* Connect point 4 to point 0 */
GP142_lineP(BLACK,polygon[4],
polygon[5],0);
passed by reference (address is copied)
( from a single structure, all the
members of the struct are copied)
142 T -5

6. Another example Sorting an array of structures typedef struct {
char name[MAX_NAME + 1];
int id;
double score; }
student_record;
Given an array of struct
student_record a[5];
sort a by score
use insertion sort on a[].score
sort a by alphabetical order of the
names
use insertion sort on a[].name
(compare using strcmp)
142 T - 6

7. char name[MAX_NAME + 1]; int id; double score; } student_record; ...
Type Quiz
typedef struct {
char name[MAX_NAME + 1];
int id;
double score; }
student_record;
...
student_record a[MAX_STUDENTS];
Expression
Type a
student_record *
a[0]
student_record
a[5].name
char *
a[4].id
int
&a[6].score
double *
a[2].name[1]
char
a->score
double
142 T - 7