Structures

We know that variables can hold a piece of information and arrays can hold a number of pieces of information of same type/ these tow data types can handle a great variety of situations. Often, we need to deal with entities that are collection of dissimilar data types. For example, to store data about a book, we might want to store its name (a string), its price (a float) and number of pages in it (an int). If data about three such books are to be stored, then we can follow two approaches:

a) Construct individual arrays, ne for storing names, another for storing prices and still another for storing number of pages.
b) Use a structure variable.

• A better way of organizing the data is to create a new user-defined data type that contains all the pieces of data organized into one structure
• C provides a data structure called a struct that allows you to create new data types
• Keyword ‘struct’ is used to declare structure.
• The new data type is an organized aggregate of other data types
• A struct has a name (e.g., structureName)
• The variables which are declared inside the structure are called as ‘members of structure’.
• A struct has members or fields, which can be any data types, such as char, int, float, string, array, bit field, and other struct

Syntax:
struct structure_nm
{
<data-type> element 1;
<data-type> element 2;
– – – – – – – – – – –
– – – – – – – – – – –
<data-type> element n;
}struct_var;

Note:
1. Structure is always terminated with semicolon (;).
2. Structure name as emp_info can be later used to declare structure variables of its type in a program.

Things to remember:

• Declaration of Structure reserves no space.
• It is nothing but the “Template / Map / Shape” of the structure.
• Memory is created, very first time when the variable is created / Instance is created.

Syntax to create a variable for a structure: struct structure_name , ……..

Ways of Declaring Structure Variable / Structure Instance:
Way 1 : Immediately after Structure Template
struct date
{
int date;
char month[20];
int year;
} today; // ‘today’ is name of Structure variable

Way 2 : Declare Variables using struct Keyword
struct date
{
int date;
char month[20];
int year;
};
struct date today;
/*———————————–
date : Name of Structure
today : Structure Variable
———————————- */
Accessing structure members: A structure contains many elements. Each elements of a structure can
be referred to / accessed by using the component selection operator “.” (Dot).
Syntax:
structure_var.member;

#include <stdio.h>
#include <conio.h>
struct comp_info
{
char nm[100];
char addr[100];
}info;
void main()
{
clrscr();
printf(“\n Enter Company Name : “);
gets(info.nm);
printf(“\n Enter Address : “);
gets(info.addr);
printf(“\n\n Company Name : %s”,info.nm);
printf(“\n\n Address : %s”,info.addr);
getch();
}

Memory map of structure elements: The structure elements are always stored in the contiguous
locations.

Array in Structures: We can also include arrays as structure elements, but accessing of such kind of elements is bit complex as shown below.
#include <stdio.h>
struct result{
int rno;
int mrks[5];
char name[20];
}res;
void main(){
int i,total;
total = 0;
printf(“\nEnter Name and Roll Number : “);
scanf(“%s%d”,res.name,&res.rno);
printf(“\nEnter Marks of 3 Subjects : “);
for(i=0;i<3;i++){
scanf(“%d”,&res.mrks[i]);
total = total + res.mrks[i];
}
printf(“\nname=%s\nRoll Number : %d”,res.name,res.rno);
printf(“\nMarks are :”);
for(i=0;i<3;i++){
printf(” \t%d”,res.mrks[i]);
}
printf(“\n\n\t Total is : %d”,total);
}
Array of structures: To store more than one record of a structure under same name, we can also creates an array variable to the corresponding structure. The storage of elements in array of structures would be as follows.

#include < stdio.h >
#include < conio.h >
struct emp
{
int empno;
char name[10];
int sal;
}e1[5];
void main()
{
int i;
clrscr();
for(i=0;i < 5;i++)
{
printf(“Enter the empno\n”);
scanf(“%d”,&e1[i].empno);
printf(“Enter the name\n”);
flushall();
gets(e1[i].name);
printf(“Enter the salary\n”);
scanf(“%d”,&e1[i].sal);
}
printf(“The record is\n”);
for(i=0;i < 5;i++)
{
printf(“\n %4d”,e1[i].empno);
printf(“%8s”,e1[i].name);
printf(” %4d\n”,e1[i].sal);
}
getch();
}

Copying of structure elements:

The values of a structure variable can be assigned to another structure variable of the same type using the assignment operator. The elements of the structure can be copied piece-meal or all at once. This is illustrated in the following example:
#include <stdio.h>
struct emp
{
int eno;
char ename[50];
float esal;
};
int main()
{
int i;
struct emp e1={1001,”naresh”,50000};
struct emp e2,e3;
e2.eno=e1.eno;
strcpy(e2.ename,e1.ename);
e2.esal=e1.esal;
e3=e2;
printf(“\n%d\t%s\t%f\n”,e1.eno,e1.ename,e1.esal);
printf(“\n%d\t%s\t%f\n”,e2.eno,e2.ename,e2.esal);
printf(“\n%d\t%s\t%f\n”,e3.eno,e3.ename,e3.esal);
return 0;
}