Structures & Union
Structures are a
form of storage like arrays. The difference between an array and a structure is
in an array all components are of the same type where in a structure you can
have different types of data. In general an object may need a variety of data
types, for example to keep record of a student's marks we need - name, roll no,
marks etc. To store these set of data under
a single variable name as Student and it is possible to access all these
parameters under one name as student. All these can be achieved by using a data type
called a Structure. A Structure is a
group of one or more variables, usually of various types, and identified by a
single name.
Declare a Structure
To declare a
structure one has to first define the contents of the structure. This will then be used as a template to
declare variables of that particular structure.
struct student
{ char name[20] ;
int roll,eng,science,maths;
} stud;
Here, student is
the name of the structure, also known as structure tag and stud is structure
label or structure variable. A structure label can be created later by using
structure name, like this struct student stud;
To access elements
in a structure, a record selector (.) is use.
To declare
additional variables of the same type, use of the keyword "struct"
followed by the <struct type name>, followed by the variable
names.
Structures can
contain other structures as members, it is known as nested structure.
Example :
struct date_of_birth {
int dd,mm,yy;
};
struct personal {
char name[20],address[30];
struct date_of_birth dob;
};
Arrays of
structures
The arrays of basic
types such as integers and floats are allowed in C, so are arrays of
structures. An array of structures is declared in the usual way:
struct student
{ char name[20] ;
int roll,eng,science,maths;
} stud[5];
Using typedef we
can create an "alias" types from structure label(variable).
Example:
typedef struct
{ char name[20] ;
int roll,eng,science,maths;
} student;
student stud;
Unions are declared
in the same fashion as structs, but have a fundamental difference. Only one
item within the union can be used at any time, because the memory allocated for
each item inside the union is in a shared memory location.
union student
{ char name[20] ;
int roll,eng,science,maths;
} stud;
Different
Between Array and Structure
Array
|
Structure
|
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Different
Between Structure and Union
Structure
|
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Example of Union
#include <stdio.h>
#include <conio.h>
void main()
{
union
books
{
char
bname[20],author[20];
int
nc;
}book;
clrscr();
printf("\nEnter
Book Name... ");
gets(book.bname);
printf("\nName
: %s ",book.bname);
printf("\nEnter
Author Name... " );
gets(book.author);
printf("\nAuthor
Name :\n",book.author);
printf("\nEnter
the no. copies...");
scanf("%d",&book.nc);
printf("\nNo.
of Copies : %d\n",book.nc);
getch();
}
Example of Simple Structure
#include <stdio.h>
#include <conio.h>
void main()
{
struct
books
{
char
bname[20],author[20];
int
nc;
}book;
clrscr();
printf("\nEnter
Book Name... ");
gets(book.bname);
printf("\nEnter
Author Name... " );
gets(book.author);
printf("\nEnter
the no. copies...");
scanf("%d",&book.nc);
printf("\nAuthor
Name :\n",book.author);
printf("\nName
: %s ",book.bname);
printf("\nNo.
of Copies : %d\n",book.nc);
getch();
}
Example of Array / Nested
Structure
#include <stdio.h>
#include <conio.h>
void main()
{
struct
date
{
int
dd,mm,yy;
};
struct
emp
{
int
ecode;
char
name[20];
struct
date jd;
float
sal;
}em[10];
int
i,n;
float
s;
clrscr();
printf("\n\tEnter
Nos. of Employee [below 10] : ");
scanf("%d",&n);
for(i=0;i<n;i++)
{
printf("\n\tEnter
Employee Code : ");
scanf("%d",&em[i].ecode);
printf("\n\tEnter Employee
Name : ");
fflush(stdin);
gets(em[i].name);
fflush(stdin);
printf("\n\tEnter
Employee Date of Birth : ");
printf("\n\t\tEnter
Day : ");
scanf("%d",&em[i].jd.dd);
printf("\n\t\tEnter
Month : ");
scanf("%d",&em[i].jd.mm);
printf("\n\t\tEnter
Year : ");
scanf("%d",&em[i].jd.yy);
printf("\n\tEnter Employee
Salary : ");
scanf("%f",&s);
em[i].sal=s;
}
printf("\n\n\t The
data \n");
printf("\n------------------------------------------------------------");
printf("\n Code
Name Date of Join Salary");
printf("\n------------------------------------------------------------");
for(i=0;i<n;i++)
{
printf("\n %d\t
%-20s\t%2d-%2d-%4d\t%8.2f",em[i].ecode,em[i].name,em[i].jd.dd,em[i].jd.mm,em[i].jd.yy,em[i].sal);
}
printf("\n------------------------------------------------------------");
getch();
}
Sorting with Array Structure
#include <stdio.h>
#include <conio.h>
struct
report
{
char
name[20];
int
marks;
} rep[3],temp;
void
disp()
{
int
i;
for(i=0;i<3;i++)
{
printf("\nName
: %s
Marks :
%d",rep[i].name,rep[i].marks);
}
}
void
main()
{
int
i,j;
clrscr();
for(i=0;i<3;i++)
{
printf("\nEnter Name :
");
fflush(stdin);
gets(rep[i].name);
printf("\nEnter
Total Marks : ");
scanf("%d",&rep[i].marks);
}
printf("\nOriginal
\n");
disp();
for(i=0;i<3;i++)
{
for(j=0;j<3;j++)
{
if(rep[i].marks>rep[j].marks)
{
temp=rep[i];
rep[i]=rep[j];
rep[j]=temp;
}
}
}
printf("\n\nSorted
in Dscending Order\n");
disp();
getch();
}
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