Introduction to Structures ~ GNIITHELP

Introduction to Structure

Structure is a user-defined data type in C which allows you to combine different data types to store a particular type of record. Structure helps to construct a complex data type in more meaningful way. It is somewhat similar to an Array. The only difference is that array is used to store collection of similar datatypes while structure can store collection of any type of data.

Structure is used to represent a record. Suppose you want to store record of Student which consists of student name, address, roll number and age. You can define a structure to hold this information.

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Defining a structure

struct keyword is used to define a structure. struct define a new data type which is a collection of different type of data.

Syntax :

struct structure_name
{
 //Statements
};

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Example of Structure

struct Book
{
 char name[15];
 int price;
 int pages;
};

Here the struct Book declares a structure to hold the details of book which consists of three data fields, namely name, price and pages. These fields are called structure elements or members. Each member can have different data type,like in this case, name is of char type and price is of int type etc. Book is the name of the structure and is called structure tag.

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Declaring Structure Variables

It is possible to declare variables of a structure, after the structure is defined. Structure variable declaration is similar to the declaration of variables of any other data types. Structure variables can be declared in following two ways.

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1) Declaring Structure variables separately

struct Student
{
 char[20] name;
 int age;
 int rollno; 
} ;

struct Student S1 , S2;   //declaring variables of Student

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2) Declaring Structure Variables with Structure definition

struct Student
{
 char[20] name;
 int age;
 int rollno; 
} S1, S2 ;

Here S1 and S2 are variables of structure Student. However this approach is not much recommended.

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Accessing Structure Members

Structure members can be accessed and assigned values in number of ways. Structure member has no meaning independently. In order to assign a value to a structure member, the member name must be linked with the structure variable using dot . operator also called period or member access operator.

struct Book
{
 char name[15];
 int price;
 int pages;
} b1 , b2 ;

b1.price=200;      //b1 is variable of Book type and price is member of Book

We can also use scanf() to give values to structure members through terminal.

scanf(" %s ", b1.name);
scanf(" %d ", &b1.price);

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Structure Initialization

Like any other data type, structure variable can also be initialized at compile time.

struct Patient
{
 float height;
 int weight;  
 int age; 
};

struct Patient p1 = { 180.75 , 73, 23 };    //initialization

or

struct patient p1;
p1.height = 180.75;     //initialization of each member separately
p1.weight = 73;
p1.age = 23;

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Array of Structure

We can also declare an array of structure. Each element of the array representing a structure variable. Example : struct employee emp[5];

The above code define an array emp of size 5 elements. Each element of array emp is of type employee

#include<stdio.h>
#include<conio.h>
struct employee
{
 char ename[10];
 int sal;
};

struct employee emp[5];
int i,j;
void ask()
{
 for(i=0;i<3;i++)
 {
  printf("\nEnter %dst employee record\n",i+1);
  printf("\nEmployee name\t");
  scanf("%s",emp[i].ename);
  printf("\nEnter employee salary\t");
  scanf("%d",&emp[i].sal);
 }
 printf("\nDisplaying Employee record\n");
 for(i=0;i<3;i++)
 {
  printf("\nEmployee name is %s",emp[i].ename);
  printf("\nSlary is %d",emp[i].sal);
 }
}
void main()
{
 clrscr();
 ask();
 getch();
}

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Nested Structures

Nesting of structures, is also permitted in C language.

Example :

struct student
{
 char[30] name;
 int age;
   struct address
    {
     char[50] locality;
     char[50] city;
     int pincode;  
    };
}; 

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Structure as function arguments

We can pass a structure as a function argument in similar way as we pass any other variable or array.

Example :

#include<stdio.h>
#include<conio.h>
struct student
{
 char name[10];
 int roll;
};
void show(struct student st);
void main()
{
 struct student std;
 clrscr();
 printf("\nEnter student record\n");
 printf("\nstudent name\t");
 scanf("%s",std.name);
 printf("\nEnter student roll\t");
 scanf("%d",&std.roll);
 show(std);
 getch();
}

void show(struct student st)
{
 printf("\nstudent name is %s",st.name);
 printf("\nroll is %d",st.roll);
}