Types of Data Structure

In computer science, a stack is a last in, first out (LIFO) abstract data type and data structure. A stack can have any abstract data type as an element, but is characterized by only two fundamental operations: push and pop. The push operation adds to the top of the list, hiding any items already on the stack, or initializing the stack if it is empty. The pop operation removes an item from the top of the list, and returns this value to the caller. A pop either reveals previously concealed items, or results in an empty list. A stack is a restricted data structure, because only a small number of operations are performed on it. The nature of the pop and push operations also means that stack elements have a natural order. Elements are removed from the stack in the reverse order to the order of their addition: therefore, the lower elements are typically those that have been in the list the longest. Data Structure Data structure is collection of data elements which are characterised by accessing functions. The accessing functions are used to store  and  retrieve data elements. For example if  the  data  is organised  as an array A of 100 elements then it's  elements  are represented  as A(1),A(2),.....A(100). In this example  accessing function is A(K), which refers to Kth element of the array A. Types of data structures Data structures can be classified as : 1. Primitive data structures Basic data types such as integer,real ,character and boolean  are known as primitive data structures or simple data types. They are known  to be simple data types as they consists of those  charac ters that can not be divided. 2. Non-Primitive data structures The  simplest example of the non-primitive data structure is  the processing of complex numbers. Very few computers are capable  of doing  arithmetic  on complex numbers. The  other  examples  are linked-lists,stacks,queues,trees and graphs. Logical versus physical implementation Logical implementation At  the logical level, the user treats the given data whether  it is  primitive or structured from programming point of  view.  The user may not have any knowledge about the storage of data in  the memory  or how the operations are performed on this data.  For  a user,  logically 2*3=6. He knows that 2*3 gives the result 6  But he  is  not aware where and how the  operations,  namely  2,3,and multiplication  are stored in the memory or how the  computer  is performing this operation. Physical implementation By  the physical implementation of data structure , it  is  meant  the mode of storage of data. This physical implementation of data  structure is discussed below : There  are many modes of stroage of data in computer memory.  For  example integers are stored in : 1. Signed bit magnitued form 2. One's complement form 3. Two's complement form 4. Binary coded decimal(BCD). This  knowledge of physical storage of data along with the  valid  opertaions  permitted,  permits the user to create ,  access  and  change the data.