#include <stdio.h>
#include <stdlib.h>
//declaring the fuctions I will be needing.
void displayList();
void Insert_AppendList();
void obtainList();
void clearList(); //without memset
 
int list[21];   //declaring some global vars, so I can use between funtions.
int choice,indexChoice,addedNumber,obtained,i=1;
	
int main()
{
	while (1) //infinite loop to wrap back to the menu.
	{	             //making output menu-styled.
	fprintf(stdout,"\n////////////////////////////////////////////\n// 1.Build\t  2.Display\t3.Insert \n// 4.Append into  5.Obtain from\t6.Clear\n// 7.Quit\n////////////////////////////////////////////\nMatch the list options menu number to the desired list and input HERE:  ");
	scanf("%d",&choice); 
	switch (choice) //switch statement to map menu choice to processes.
	{		
		case 1:
		while (list[i-1]!=-1)
		{
			if (i>=21) //limit to 20 numbers in index
			{
				list[21]=-1;
				printf("\nYour building list is full.\n");
				break;
			}

			if (i==1) //give directions first time around
			{
				printf("\nEnter numbers until you are done building your list (20 numbers max). When your list is done enter -1 to singnal the end of the list. INPUT FIRST NUMBER: ");
			}
			else 
			{
				printf("Next number: "); // continue prompting numbers
			}
			scanf("%d",&list[i]);
			i++; // go tonext element in array
		}
		break;
		case 2:
		displayList(); // print out list
		break;
		case 3:
		if(list[1]==0) // assume there is no list if first number is 0
	    {
			printf("OOPS! It looks like you don't have a list yet.\n");
			break;
		}
		printf("Where would you like to insert?(1-20): ");
		scanf("%d",&indexChoice);
		indexChoice--;
		printf("[Enter Number] index%d: ",indexChoice);
		scanf("%d",&addedNumber);
		Insert_AppendList(); //use to capture index before
		break;
		case 4:
		if(list[1]==0)
		{
			printf("OOPS! It looks like you don't have a list yet.\n");
			break;
		}
		printf("Where would you like to append?(1-20): ");
		scanf("%d",&indexChoice);
		indexChoice++;
		printf("[Enter Number] index%d: ",indexChoice);
		scanf("%d",&addedNumber);
		Insert_AppendList();//used to capture index after
		break;
		case 5:
		if(list[1]==0)
		{
			printf("OOPS! It looks like you don't have a list yet.\n");
			break;
		}
		printf("Which index number to obtain from?(1-20): ");
		scanf("%d",&indexChoice);
		obtainList(); 
		displayList();
		printf("\nNumber Obtained: %d\n",obtained); //print number obtained with function
		break;
		case 6:
		clearList();
		printf("\nLIST CLREARED\n");
		break;
		case 7:
		printf("\nList's will not be saved, ARE YOU SURE?\n(1.Yes|2.No)\n");
		scanf("%d",&indexChoice);
		if (indexChoice==1) //exit if selected with 1, otherwise continue with loop.
		exit(0);
		break;
		default://The default if none of the menu options are selected.
		fprintf(stderr,"\nINVALID MENU OPTON, read the menu and try again.\n");
		exit(1);
		break;
	}
}		
	return(0);
}

void displayList()
{						
	i=1;
	while(list[i]!=-1)
	{
		if(list[1]==0)
		{
			printf("OOPS! It looks like you don't have a list yet.\n");
			break;
		}
		else
		{
			printf("index%d: %d\n",i,list[i]); //navigate and print array
			i++;                               //until end of list marker.
		}
	}
}
void Insert_AppendList()
{
	int holder,holder2;
	i=indexChoice;
	if(i<21)
	{
		holder=list[i];
		list[i]=addedNumber;
		i++;
		while(i<21) // Buffers to insert and shift w/o losing data.
		{	
			holder2=list[i];
			list[i]=holder;
			i++;
			holder=list[i];
			list[i]=holder2;
			i++;
		}
	}
	else
	printf("\nYou are limited to 20 index's.\n");//incase try to store past 20
}
void obtainList()
{
	obtained=list[indexChoice]; // to obatin and erase.
	list[indexChoice]=0;
}
void clearList()
{
	i=1;
	while(i<=20)
	{
		list[i]=0;//set everything to 0.
		i++;
	}
}