1. By C. Shing ITEC Dept Radford University
Chapter 6 Structures
By C. Shing
ITEC Dept
Radford University

2. Objectives Understand how to use structures
Understand how to call function by passing
structures
Understand how to use unions

3. Structure A record that can store different data types
Declared data type (struct structure_name) first as
struct [structure_name] {
type1 fieldname1;
… } [variable_lists];
Then define a new type by
typedef struct structure_name structure_type; or
typedef struct {
… } structure_type;

4. Structure (Cont.) Example: struct student_record { char lastname[30];
char firstname[15];
float gpa; };
typedef struct student_record student_rec;

5. Structure (Cont.) Declared variables then as Or use Example:
struct structure_name variable_list;
Or use
structure_type variable_list;
Example:
struct student_record student1, student2;
struct student_record student[100]; or
student_rec student[100];…

6. Initialize Structure Similar to initialize an array
Fill in 0 or NULL if not enough data
Example:
student_rec student1={“Doe”, “John”, 2.0};
student_rec student_any;

7. Read in Structure from Keyboard
Example:
scanf(“%s%s%f”, student1.lastname,
student1.firstname, &student1.gpa);
// data: Doe John 2.0
Example1

8. Structure Assignment Assign field:
student_any.lastname=student1.lastname;
Example: Program, Data
Assign whole structure:
Example:
student_any= student1;

9. Pointer and Structure If a pointer p to a stucture_type variable, then
to access a field (or member), use
p -> fieldname Or
(*p).fieldname
Example 2

10. Pointer and Structure (Cont.)
Example:
student_rec student1={“Doe”, “John”, 2.0},
*student_pointer=&student1;
Then student_pointer->lastname = “Doe”;
(*student_pointer).firstname = “John”;
student_pointer->gpa=2.0;
(student_pointer->firstname)[3]=‘n’;
(*(student_pointer->firstname))+2=‘L’;

11. Pass Structure to Function
Use pass-by-value: pass a copy of structure,
Default, not efficient
If structure is changed after function call, must return the structure_type result
The returned result must be assigned back to the original variable
Example:
student1=change_gpa (student1);
student_rec change_gpa (student_rec student_any) {
printf(“Please enter new gpa:\n”);
scanf(“%f”, &student_any.gpa);
return student_any; }
Example 3

12. Pass Structure to Function (Cont.)
Use pass-by-reference: pass in pointer,
very efficient
Example:
change_gpa (&student1);
void change_gpa (student_rec *student_pointer) {
printf(“Please enter new gpa:\n”);
scanf(“%f”, &student_pointer->gpa); }
Example 4

13. Sort Structures Problem: input data into array of structures
And then sort them
Data:
1 15.0
2 15.0
3 11.0
4 9.0
5 9.0

14. Sort Structures (Cont.)
struct request {
int number;
double duration; };
typedef struct request requesttype;
void input(requesttype request[], int *count);

15. Sort Structures (Cont.)
int main(void) {
requesttype request[1000];
int count=0; …
input(request, &count);
sort_struct(request, count); }

16. Sort Structures (Cont.)
void input(requesttype request[], int *count) {
int i;
for (i=0;
scanf("%d", &request[i].number), request[i].number !=0; i++)
scanf("%lf", &request[i]. duration); …
(*count)++; }

17. Sort Structures (Cont.)
void sort_struct (requesttype w[], int n) {
int i, j;
for (i=0; i<n; ++i)
for (j=i+1; j<n;++j)
if (w[i].duration > w[j].duration)
swap (&w[i], &w[j]); }

18. Sort Structures (Cont.)
void swap (requesttype *s, requesttype *t) {
requesttype tmp;
tmp=*s;
*s=*t;
*t=tmp; }

19. Sort Structures – Another Way (Cont.)
void sort_struct (requesttype w[], int n) {
int i, j;
for (i=0; i<n; ++i)
for (j=i+1; j<n;++j)
if (w[i].duration > w[j].duration)
swapInt (&w[i], &w[j]);
swapDouble (&w[i], &w[j]); }

20. Sort Structures – Another Way (Cont.)
void swapInt (requesttype *s, requesttype *t) {
int tmp;
tmp=s->number;
s->number=t->number;
t->number=tmp; }

21. Sort Stuctures – Another Way (Cont.)
void swapDouble (requesttype *s, requesttype *t) {
double tmp;
tmp=s->duration;
s->duration=t->duration;
t->duration=tmp; }

22. Example Helpful Code Data Sort Student Name and Grades Structure;
Program, Data

23. Operators Priority Operator Same Priority Rule
(),postfix++/--,[],.,->
Left to right
Unary +/-, prefix++/--, !, ~,&, *
Right to left
*, /, %
+, -
<<, >>
<, >, <=, >=
==, !=

24. Operators Priority (Cont.)
Same Priority Rule
& ^ |
&&
Left to right || ?:
Right to left ,

25. Union Create a new type (union union_name)
by union sets of different data types
Declare as
union union_name {
type1 variable1;
…; };

26. Union (Cont.) Example: union number { long i; float f;};
typedef union number number;
number number1, number2;
number1.i=100;
number2.f=-1.23;
printf(“%d%f\n”, number1.i, number1.f);
printf(“%d%f\n”, number2.i, number2.f);

27. Example
Helpful Code

28. Structure with Bit Fields
Purpose: reduce space
Declare structure data types using bits fields as
struct structure_name {
unsigned field1: number of bits,
field2: number of bits,
:0, // align to next word
…; };
typedef struct structure_name structure_type;
structure_type variable_list;

29. Structure with Bit Fields (Cont.)
Example: Create a small_number that has 7 bits
of signed integer or float
struct small_number {
unsigned int_sign: 1, // 0: positive, 1: negative using 2s complement
i : 6,
:0, // align to next word
float_sign: 1,
f : 6; // don’t worry align at the end };
typedef struct small_number small_number;
small_number s_number1;

30. Structure with Bit Fields (Cont.)
Example: (Cont.)
// assign 23 to snumber1
snumber1.int_sign=0;
snumber1.i=23;

31. Data Structure - stack Stack: insert (push) and delete (pop)
at the same place (top).

32. Example 1- stack Write a program that implements a stack of
characters using an array.
typedef struct stack {
char s[STACKSIZE];
int top;
} stack;

33. Example 1– stack (Cont.) void clear_stack (stack *stk) {
stk->top=-1; };
void push(char c, stack *stk) {
stk->top++;
stk->s[stk->top]=c; }

34. Example 1– stack (Cont.) char top (const stack *stk) {
return (stk->s[stk->top]); };
char pop (stack *stk) {
return (stk->s[stk->top--]); }

35. Example 1– stack (Cont.) int is_full (const stack *stk) {
return ((int) (stk->top == STACKSIZE-1)); };
int is_empty (const stack *stk) {
return ((int) (stk->top == -1));

36. Example 2- stack Write a program that implements a stack of
integers using a linked list.
typedef struct node {
int info;
struct node *next;
} node;
typedef struct stack {
node * head;
} stack;;

37. Example 2– stack (Cont.) void clear_stack(stack *stk) {
stk->head=NULL; }

38. Example 2– stack (Cont.) // insert item to head, delete from head
void push (int item, stack *stk) {
node *newnode;
newnode = malloc(sizeof(node)); // dynamically create a new node
if (!newnode)
printf("No memory is available.\n");
else
newnode->info= item;
newnode->next= stk->head;
stk->head=newnode;
} // else }

39. Example 2– stack (Cont.) int top (const stack *stk) {
return (stk->head->info); }

40. Example 2– stack (Cont.) int pop (stack *stk) { int item;
node *deletednode;
deletednode=stk->head;
item=deletednode->info;
stk->head=deletednode->next;
free(deletednode);
return item; }

41. Example 2– stack (Cont.) int isempty (stack *stk) {
return (stk->head == NULL); }

42. Example 2– stack (Cont.) void output (stack stk) {
printf (" ”);
Printf(“All items in the stack: \n");
for (;!isempty(&stk);)
printf("%d\n", top(&stk));
stk.head=(stk.head)->next; }

43. Example 2– stack (Cont.)
Helpful Code
Data

44. Data Structure - Queue Insert (enqueue) at the tail and
Delete (dequeue) at the head.

45. Example - Queue Write a program that implements a queue of
integers using a linked list.
struct node {
int info;
struct node *next; };
typedef struct node node;
node *head=NULL, *tail=NULL; // initialize

46. Example – Queue (Cont.) int isempty (node * head) {
return (head == NULL); }

47. Example – Queue (Cont.) // insert item to tail, delete from head
void enqueue (node **ptrhead,
node **ptrtail, int item) {
node *newnode;
// dynamically create a new node
newnode = malloc(sizeof(node));
if (!newnode)
printf("No memory is available.\n");

48. Example – Queue (Cont.)
// insert item to tail, delete from head (Cont.)
else {
newnode->info= item;
newnode->next=NULL;
if (isempty(*ptrhead)) // if (!(*ptrhead)) means head is equal to NULL
*ptrhead=newnode;
(*ptrtail)->next=newnode;
*ptrtail=newnode;
} // else
} // enqueue

49. Example – Queue (Cont.) // delete from head and return info
int dequeue (node **ptrhead, node **ptrtail) {
int item;
node *deletednode;
deletednode=*ptrhead;
item=deletednode->info;
*ptrhead=deletednode->next;
if (isempty(*ptrhead))
*ptrtail=NULL;
free(deletednode);
return item; }

50. Example – Queue (Cont.) void output (node *head) {
printf (" ”);
printf(“All items in the queue: \n");
for (;!isempty(head);) // for (;head != NULL;)
printf("%d\n", head->info);
head=head->next; }

51. Example – Queue (Cont.) Program (node is int) Code Data
Program (node is a structure) Code

52. Data Structure – Binary Tree
Each (parent) node has at most 2 children
Binary search tree:
right child node value > parent node value > left
child value

53. Example – Binary search tree
Write a program that implements a
binary search tree of integers using a linked list.
typedef struct node {
struct node *left;
int info;
struct node *right;
} node;

54. Example – Binary search tree (Cont.)
typedef struct tree {
node * root;
} tree;

55. Example – Binary search tree (Cont.)
void clear_tree(tree *bst) {
bst->root=NULL; }

56. Example – Binary search tree (Cont.)
void insert (int item, tree *bst) {
node *newnode;
if (bst->root == NULL) // base case
newnode = malloc(sizeof(node)); // dynamically create a new node
if (newnode == NULL)
printf("No memory is available.\n");
else
newnode->info= item;
newnode->left= NULL;
newnode->right= NULL;
bst->root=newnode;
printf("%d\n", bst->root->info); }

57. Example – Binary search tree (Cont.)
Else // inductive case {
if (item> bst->root->info)
bst->root=bst->root->right;
else
bst->root=bst->root->left;
insert(item, bst); }
} // insert

58. Example – Binary search tree (Cont.)
Helpful Code
Data

59. Practice Given struct student { char lastname[15]; long studentid;
char grade; };
struct student tmp, *p=&tmp;
tmp.grade='A';
tmp.lastname="Casanova";
tmp.studentid=910017;

60. Practice (Cont.) Find the values of the following table:
Expression Value
________ _____
tmp.grade
tmp.lastname
(*p).studentid
*p->lastname+1
*(p->lastname+2)

61. Practice (Cont.) Find the values of the following table:
Expression Value
________ _____
tmp.grade ‘A’
tmp.lastname “Casanova”
(*p).studentid
*p->lastname+1 ‘D’
*(p->lastname+2) ‘s’

62. References Deitel & Deitel: C How to Program, 4th ed.,
Chapter 10 & 12, Prentice Hall