Structure and Unions & Memory Allocation

Structure 

Is a data type to store a group of data with various of data type.

Structure Declaration

1. 
struct name_structure {
   dataType1 name_field1;
   dataType2 name_field2;
   …
} name_variable_structure ;

2. 

struct name_structure  name_variable_structure; 

Accessing Structure

Element of a structure can be accessed using dot operator

struct mhs {

  char nim[9];

  char name[26];

  float gpa;

};

int main (){

  struct mhs lia;

  gets(lia.name);

}

Structure Initialization

Syntax:

struct struct_name variable = {value_1, …, value_m};

struct employee info = {1,"B. Smith"};

Array of Structure

Structure data type can only contain one record. But real world problem needs group of records. So it's a structure inside a structure. 

Example:

struct Dob{

  int date, month, year;

};

struct Account {

   int accountNo;

   char accountType;

   char name[31];

   long credit;

   struct Dob lastTrans;

};

//Array of structure

struct Account customer[100];

Union

A union is a special data type available in C that allows to store different data types in the same memory location. You can define a union with many members, but only one member can contain a value at any given time. Unions provide an efficient way of using the same memory location for multiple-purpose.

Memory Allocation

Acquiring some memory space (RAM) managed by the OS to be used by the program.