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So far, we have seen one kind of compound (user defined) data type -
the array and in Chapters 
and have
seen how we can group information into one common data structure.
However, the use of arrays is limited to cases where all of
the information to be grouped together is of the same type.
In this chapter we present the other compound data type provided
in C - the structure, which removes the above limitation.
We will discuss structures, pointers to structures, and arrays
of structures.
As with our previous data types, we will see how such structures
can be declared; how information in them can be accessed,
and how we can pass and return structures in functions.
We will also see how arrays of structures are sorted and searched.
We illustrate these points with several example programs.
Finally, we will introduce unions which are similar to structures;
however, the elements in the union share the same memory cells.
In a union, different types of data may be stored in a variable
but at different times.