The new node is created with the help of pointer temp. The malloc () function allocates memory
of structure doubly size to pointer temp. The entered number is assigned to member variable
number. The next link field is assigned a NULL value using the statement temp->next=NULL.
The first four statements of the function form () are used for creation of the new node and the
remaining part is for adjusting link fields.
Consider the following statements.
1) temp->p=NULL: This statement is used to assign NULL value to the previous pointer. As it is
the first node and no previous link is available.
2) first->p=tem
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