Structures and file management in c language

Structures And File Management
Introduction
 Derived data type : int,float,char,double, are the primitive data types .
 Using these primitive data types we can derive other data types and such data types
derived from basic types are called derived data types.
Type definition
 Typedef is a keyword that allows the programmer to create new data type name for an
already existing datatype.
 Syntax:
typedef old datatype newdatype ;


Example: typedef int MARKS;
typedef float AMOUNT;

Example:
 Program to compute simple interest using typedef definition
#include<stdio.h>
typedef float AMOUNT;
typedef float TIME;
typedef float RATE;
void main( )
{
AMOUNT p,si;
TIME t;
RATE r;
printf(“enter the value of p,t,r\n”);
scanf(“%f%f%f”,&p,&t,&r);
si=(p*t*r)/100;
printf(“si=%f\n”,si);
}

Advantages of typede:
1. Provide a meaningful way of declaring variable
2. Increases readability of program
3. A complex and lengthy declaration can be reduced to short and meaningful declaration
4. Helps the programmer to understand source code easily.

, Structures
 Definition: A structure is defined as a collection of variables of same data type or
dissimilar datatype grouped together under a single name.

Syntax Example
struct tagname struct student
{ {
datatype member1; char name[10];
datatype member2; int usn;
datatype member3; float marks;
} };

where
struct is a keyword which informs the compiler that a structure is being defined
tagname: name of the structure
member1,member2: members of structure:
type1,type 2 : int,float,char,double

Structure Declaration
As variables are declared ,structure are also declared before they are used:

Three ways of declaring structure are:
 Tagged structure
 Structure without tag
 Type defined structures

1.Tagged structure

syntax Example
struct tag_name struct student
{ {
data type member1; char name[20];
data type member2; int usn;
-------------------- float marks;
-------------------- };
};

Declaration of structure variables
struct tagname v1,v2,v3…vn; struct student s1,s2,s3;

, 2.structure without tagname
syntax Example
struct struct
{ {
data type member1; char name[20];
data type member2; int usn;
; float marks;
-------------------- }s1,s2;
--------------------
}v1,v2,v3;



3.Type defined structure
syntax Example
typedef struct typedef struct
{ {
data type member1; char name[20];
data type member2; int usn;
-------------------- float marks;
-------------------- }STUDENT;
}TYPE_ID;




Declaring structure variables

TYPE_ID v1,v2,v3…vn; STUDENT s1,s2,s3;

Memory Allocation for structure variable s1:


name(10 bytes) usn(2 bytes) marks (4 bytes)

memory allocated for a structure variable s1=memory allotted for name+usn+marks
10+2+4
16 bytes.

Structure initialization
Syntax:
struct tagname variable={v1,v2….vn};

, example
struct student s1={“sony”,123,24};
Accessing structures
 The members of a structure can be accessed by specifying the variable followed by dot
operator followed by the name of the member.
 For example,
consider the structure definition and initialization along with
memory representation as shown below:

struct student
{
char name[20];
int usn;
float marks;

} s1;
struct student s1 = {"aditi",002,40};

By specifying
Variblename . membername
Example
S1.name
S1.usn
S1.marks

Structure operations
1. Copying of structure variables
2. Arithmetic operations on structures
3. Comparision of two structures

1. Copying of structure variables
 copying of two structure variables is achieved using assignment operator.
 Consider two structure definition of student and emplpoyee

struct student struct employee
{ {
char name[20]; char ename[20];
int usn; int eid;
float marks; float salary;
}; };