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======Project: Stack library======

A project for C/C++, Data Structures, and System Programming by Karl Krauss for fall 2011.

Approximately 3 hours including taking the time to full grasp all concepts that were used, this was much simpler than doubly linked list as the "hard" parts had been figured out already.

=====Objectives=====
The purpose of this project was to create a library for stacks.

=====Prerequisites=====
In order to successfully accomplish/perform this project, the listed resources/experiences need to be consulted/achieved:

  * understand functions
  * understand pointers
  * understand structs
  * understand malloc()

=====Background=====

This was the next evolution of the doubly linked list library.  This is the stack library, taking what I learned from implementing the dl library this was much simpler.

=====Attributes=====

====Cprog attributes====

  * variables
  * pointers 
  * selection 
  * i/o 
  * repetition 
  * functions 
  * structures 
  * libraries
====Data Structures====
  * Pointers
  * Malloc/new
  * linked list
  * Doubly linked list
  * Libraries

====Systems programming====
  * Terminal I/O

=====Code=====
This is the header file: 
<code c>
#ifndef			STACK_H

#define      	STACK_H





struct node { //predefined structure with one variable (

	int value;

	struct node *next;

	struct node *prev;

};

typedef struct node Node;



struct stack {// predefined structure for use of returns in functions allow for easy access to stack.  *end is top of stack

	Node *start;

	Node *end;

};

typedef struct stack Stack;



Stack *push(Stack *myStack, int input);

Node *pop(Stack *myStack);

Node *peek(Stack *myStack);







//minimum variables needed in main: int input, Node *tmp, Node *tmp2, List *myList.



#endif
</code>

This is the code:
<code c>
typedef struct list List;

	in List: * start will be the stack and *end the top of the stack.

*/
List *push(List *myList, Node *tmp, int input);
List *pop(List *myList, Node *tmp, int i);
void peek(List *myList);
int main()
{

	List *myList;
	//Node *stack, *top
	Node *tmp;
	int i=0, input;

	//tmp = stack = top = NULL;
	myList=(List *)malloc(sizeof(List));
	myList->start =myList->end = tmp = NULL;

	printf("Please enter a value (-1 to stop): ");//puts kept printing a new line

	scanf("%d", &input);

	while (input != -1)
	{
		push(myList, tmp, input);
		i++;
		printf("Please enter a value (-1 to stop): ");
		scanf("%d", &input);

	}

	peek(myList);
	getchar();
	getchar();
	while (i != 0)//tmp = (Node *)pop(myList, tmp, i)) != NULL) 
	{

		myList=pop(myList, tmp, i);
		i--;
	}

	return 0;
}

List *push(List *myList, Node *tmp, int input)// pushing a new value onto the top of the stack
{
	myList = newNode(myList, tmp, input);

	return myList;
}

List *pop(List *myList, Node *tmp, int i)// popping value off the top of the stack
{

	int x;
	tmp = myList->start;

	for(x=1; x<i; x++)
	{
		tmp = tmp->next;
	}

	printf("value: %d\n", tmp -> value);
	deleteNode(myList, tmp, i);

	return myList;
}

void peek(List *myList)// checking to see whats on the top of the stack
{
	if(myList->start == NULL)
	{
		printf("The stack is empty\n");
	}
	else
	{
		printf("THe value at the top of the stack is: %d\n", myList->end->value);
	}
}
</code>

=====Reflection=====
  *As with doubly linked lists,  I really learned a lot.  This library was written quite some time ago and the best part is when I came back to it, I had learned enough to realize I could vastly improve upon it. Something I will possibly do in the future.
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