STRUCTURES IN C LANGUAGE

Structure: 

• Structure is a method of packing the data of different types.
• When we require using a collection of different data items of different data types in that situation we can use a structure.
• A structure is used as a method of handling a group of related data items of different data types.

A structure is a collection of variables under a single name. These variables can be of different types, and each has a name which is used to select it from the structure. A structure is a convenient way of grouping several pieces of related information together.

A structure can be defined as a new named type, thus extending the number of available types. It can use other structures, arrays or pointers as some of its members, though this can get complicated unless you are careful.

Defining a Structure

A structure type is usually defined near to the start of a file using a typedef statement. typedef defines and names a new type, allowing its use throughout the program. typedefs usually occur just after the #define and #include statements in a file.

Here is an example structure definition.

  typedef struct {

          char name[64];

          char course[128];

          int age;

          int year;

  } student;

This defines a new type student variables of type student can be declared as follows.

  student st_rec;

Notice how similar this is to declaring an int or float.

The variable name is st_rec, it has members called name, course, age and year.

Accessing Members of a Structure

Each member of a structure can be used just like a normal variable, but its name will be a bit longer. To return to the examples above, member name of structure st_rec will behave just like a normal array of char, however we refer to it by the name .

  st_rec.name

Here the dot is an operator which selects a member from a structure.

Where we have a pointer to a structure we could dereference the pointer and then use dot as a member selector. This method is a little clumsy to type. Since selecting a member from a structure pointer happens frequently, it has its own operator -> which acts as follows. Assume that st_ptr is a pointer to a structure of type student We would refer to the name member as.

  st_ptr -> name

/* Example program for using a structure*/
#include< stdio.h >
void main()
{
int id_no;
char name[20];
char address[20];
char combination[3];
int age;
}newstudent;
printf(”Enter the student information”);
printf(”Now Enter the student id_no”);
scanf(“%d”,&newstudent.id_no);
printf(“Enter the name of the student”);
scanf(“%s”,&new student.name);
printf(“Enter the address of the student”);
scanf(“%s”,&new student.address);printf(“Enter the cmbination of the student”);
scanf(“%d”,&new student.combination);printf(Enter the age of the student”);
scanf(“%d”,&new student.age);
printf(“Student information\n”);
printf(“student id_number=%d\n”,newstudent.id_no);
printf(“student name=%s\n”,newstudent.name);
printf(“student Address=%s\n”,newstudent.address);
printf(“students combination=%s\n”,newstudent.combination);
printf(“Age of student=%d\n”,newstudent.age);
}

Arrays of structure:

It is possible to define a array of structures for example if we are maintaining information of all the students in the college and if 100 students are studying in the college. We need to use an array than single variables. We can define an array of structures as shown in the following example:

structure information
{
int id_no;
char name[20];
char address[20];
char combination[3];
int age;
}
student[100];

An array of structures can be assigned initial values just as any other array can. Remember that each element is a structure that must be assigned corresponding initial values as illustrated below.

#include< stdio.h >
{
struct info
{
int id_no;
char name[20];
char address[20];
char combination[3];
int age;
}
struct info std[100];
int I,n;
printf(“Enter the number of students”);
scanf(“%d”,&n);
printf(“ Enter Id_no,name address combination age\m”);
for(I=0;I < n;I++)
scanf(“%d%s%s%s%d”,&std[I].id_no,std[I].name,std[I].address,std[I].combination,&std[I].age);
printf(“\n Student information”);
for (I=0;I< n;I++)
printf(“%d%s%s%s%d\n”, ”,std[I].id_no,std[I].name,std[I].address,std[I].combination,std[I].age);
}

Structure within a structure:

A structure may be defined as a member of another structure. In such structures the declaration of the embedded structure must appear before the declarations of other structures.

struct date
{
int day;
int month;
int year;
};
struct student
{
int id_no;
char name[20];
char address[20];
char combination[3];
int age;
structure date def;
structure date doa;
}oldstudent, newstudent;

the sturucture student constains another structure date as its one of its members.

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