Defining structure

For structure, we use struct keyword.

Syntax:
struct struct_name{ structure_member };
struct address{
      unsigned int house_number;
   char street_name[50];
    int zip_code;
      char country[50];
   };

Declaring structure

The above example only defines an address structure without create any instance of it. To create or declare a structure you have two ways:

The first way is declare a structure follows by structure definition like this:
struct struct_name {
      structure_member;
      ...
    } instance_1,instance_2 instance_n;

In the second way you can declare your structure instance at a different location in your source code after structure definition.

Syntax :

struct struct_name instance_1,instance_2 instance_n;

Complex structure

Structure can contains arrays or other structures so it is sometimes called complex structure.

For example address structure is a complex structure.
struct customer{
      char name[50];
      structure address billing_addr;
      structure address shipping_addr;
    };

The reference site for this content is http://cprogramminglanguage.net/c-structure.aspx