1 Structures

2 C gives you several ways to create a custom data type. –The structure, which is a grouping of variables under one name and is called an aggregate data type. –The “typedef” keyword, allow us to define a new user-defined type. Derived Data Type

3 Structures A structure is a collection of variables referenced under one name, providing a convenient means of keeping related information together. It allows us to organize related data of different types in one structure.

4 Structure Declaration A structure declaration forms a template that can be used to create structure objects (instances of a structure). The variables that make up the structure are called members. Usually, the members of a structure are logically related.

5 General Form struct tag { type member-name; type member-name; type member-name;... } structure-variable(s);

6 struct addr { char name[30]; char street[40]; char city[20]; char state[3]; unsigned long int zip; }; Terminated by a semicolon keyword structure tag name No variable has actually been created.

7 Structure Variable Declaration struct addr addr_info; declares a variable of type struct addr called addr_info. The compiler automatically allocates sufficient memory to accommodate all of its members.

8 Name30 bytes Street40 bytes City20 bytes State 3 bytes Zip 4 bytes Assume 4-byte long integers Memory allocated for addr_info

9 struct addr { char name[30]; char street[40]; char city[20]; char state[3]; unsigned long int zip; } addr_info, binfo, cinfo; You can declare one or more objects when declare a struct type

10 Initialization of Structures All, Extern and Static Variables including structure variables that are not explicitly initialized, are automatically initialized to 0.

11 Accessing Structure Members Individual members of a structure are accessed through the use of the Dot Operator (“.”). General form: object-name.member-name

12 See slide 9: Created 3 Struct vars. e.g.,addr_info.zip = 12345; printf("%lu", addr_info.zip); gets(addr_info.name); for(t=0; addr_info.name[t]; ++t) putchar( addr_info.name[t] );

13 Structure Assignments #include int main(void) { struct { int a; int b; } x, y; x.a = 10; y = x; /* assign one structure to another */ printf("%d", y.a); return 0; } Do not need to assign the value of each member separately

14 Array of Structs WHY? What does an array of structs allow us to do that is not possible with any other single structure?

15 Arrays of Structures To declare an array of structures, you must first define a structure and then declare an array variable of that type. struct addr addr_list[100]; printf("%lu", addr_list[2].zip); addr_list[2].name[0] = 'X';

16 Passing Structures to Functions Passing Structure Members to Functions. Passing Entire Structures to Functions

17 Passing Structure Members to Functions When you pass a member of a structure to a function, you are passing the value of that member to the function. It is irrelevant that the value is obtained from a member of a structure. struct friend { char x; int y; float z; char s[10]; } mike;

18 func(mike.x); /* passes character value of x */ func2(mike.y); /* passes integer value of y */ func3(mike.z); /* passes float value of z */ func4(mike.s); /* passes address of string s */ func(mike.s[2]); /* passes character value of s[2] */ func(&mike.x); /* passes address of character x */ func2(&mike.y); /* passes address of integer y */ func3(&mike.z); /* passes address of float z */ func4(mike.s); /* passes address of string s */ func(&mike.s[2]);/* passes address of character s[2] */

19 Passing Entire Structures to Functions Call-by-value: #include struct Example_type { int a, b; char ch; } ;

20 void f1(struct Example_type parm); int main(void) { struct Example_type arg; arg.a = 1000; f1(arg); return 0; } void f1(struct Example_type parm) { printf(''%d", parm.a); } struct_type must match

21 In Header File: cl_info.h #define CLASS_SIZE 100 struct student { char *last_name; int student_id; char grade; }; In Program File : #include “cl_info.h” MAIN( ) { struct student temp, class [CLASS_SIZE]; ….. } e.g.:To count the number of failing students in a given Class.

22 Structure Pointers When a pointer to a structure is passed to a function, only the address of the structure is pushed on the stack. This makes for very fast function calls. Passing a pointer makes it possible for the function to modify the contents of the structure used as the argument via call-by- reference.

23 Declaring a Structure Pointer Like other pointers, structure pointers are declared by placing * in front of a structure variable's name. struct addr *addr_pointer;

24 Using Structure Pointers To pass a structure to a function using call by reference. To create linked lists and other dynamic data structures that rely on dynamic allocation.

25 struct bal { float balance; char name[80]; } person; struct bal *p; /* declare a structure pointer */ p = &person;

26 The Structure Pointer Operator access the members of a structure Used to access the members of a structure via a pointer. p–>balance Forms: (*pointer-To-Struct). member or pointer-To-Struct member –>

27 struct student temp, *p = &temp; temp.grade = ‘A’; temp.last_name = “Bushker”; temp.student_id = ; struct student { char *last_name; int student_id; char grade; };

28 ExpressionEquivalentValue temp.gradep –> grade A temp.last_namep –> last_nameBushker temp.student_idp –> student_id (*p).student_id Parenthesis are necessary (dot) has higher priority than *

29 Arrays and Structures Within Structures A member of a structure can be either a single variable or an aggregate type. In C aggregate types are arrays and structures.

30 Arrays Within Structures To reference element [ 3,7] in member a of Structure y. y.a[3][7] int a[10] [10]; struct x { int a[10] [10]; /* 10 x 10 array of ints */ float b; } y;

31 Structures within Structures worker.address.zip = 93456; The C89 standard specifies that structures can be nested to at least 15 levels. struct emp { struct addr address; /* nested structure */ float wage; } worker;

32 Using sizeof to Ensure Portability Type Size in Bytes char1 int4 double8 sizeof(s_var) is 13 (8+4+1). struct s { char ch; int i; double f; } s_var; malloc(sizeof(struct s)); struct s *p; p = malloc(sizeof(struct s));

33 typedef You can define new data type names by using the keyword typedef –You are not actually creating a new data type. –You define a new name for an existing type. The primary advantage of the type definition is that it allows you to replace a complex name, such as a pointer declaration, with a mnemonic that makes the program easier to read and follow.

34 General Form: typedef type newname; typedef float BALANCE; BALANCE over_due;

35 E.g., The declaration for an array of pointers to strings. Char * stringPtrAry[20]; Typedef char * STRING; STRING StrPtrAry[20];

36 Typedef with Structures typedef typedef struct { char id[10]; char name[26]; int gradepts; } STUDENT; A typename not a variable. STUDENT pupil; void printstudent (STUDENT Stu);

37 LINKED LIST DATA STRUCTURE A Linked List is an ordered collection of data in which each element contains 2 parts: data and link. The data part holds info fields and the link is used to chain the data together. It contains a pointer that identifies the in next node the list. A Pointer variable points to the first node (HEAD) in the list. Memory for each node is allocated dynamically.

38 The Head ptr gives acess to the LINKED LIST which is a sequence of linked nodes. Data Head

39 Self-Referential Structures The node in a linked list are called self- referential structures: Each instance of the structure contains a pointer member to another instance of the same type. This gives us the ability to create our linked list structure in which one instance of a node structure points to another instance of the node structure.

40 Type Definition for a Linked List typedef int KEY_TYPE; typedef struct { KEY_TYPE key; … /* other data fields */ } DATA; typedef struct nodetag { DATA data; struct nodetag *link; } NODE; A TYPE for EACH NODE

41 Pointers to Linked Lists One of the attributes of a linked list is that its data are NOT stored with physical adjaceny- like array data is. We need to identify the first logical node in the list which we do with a pointer variable designated as the HEAD POINTER. A linked list MUST always have a head ptr and will likely have other pointers which will be used for implementing LL activities (e.g., insertions, deletions, searches …).

42 Primitive List Functions To work with a linked list we need some basic operations that manipulate the nodes. INSERT a Node: At the beginning. At the end. Anywhere in the list. DELETE a Node: At the beginning. At the end. Anywhere it is. SEARCH for a Find the location for node. above activities.

43 Inserting a New Node Steps to insert a new node: 1. Allocate memory for the new node. 2. Determine the insertion point. Implies a search function. We need to know the new nodes logical predecessor. 3. Point the new node to its successor. 4. Point the predecessor to the new node.