Pointer to pointer problem(I think)

[efronefron]

There is a problem I am having inside the AddToEnd function.

At this line:

*ptrL->ptrNext = ptrInput;

it gives this error:

lab8.c: In function ‘AddToEnd’:
lab8.c:105: error: request for member ‘ptrNext’ in something not a structure or union

Can anybody tell me why?

P.S. I realized that I do not have to pass ptrFirst and ptrLast, but this is just for the sake of practice with pointers

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

// DOCUMENT!!!!!!
struct point
{
	int x;
	int y;
	char label[21];
	struct point *ptrNext;		// self referential pointer
};

int isEmptyList(struct point *ptrF);
void PrintList(struct point *ptrF);
void ResetList(struct point *ptrF, struct point *ptrL);
void AddToBeginning(struct point **ptrF, struct point **ptrL);
void AddToEnd(struct point **ptrF, struct point **ptrL);
void InputRecord(struct point *ptrNew); // used by Add to interactively get the values from the user

struct point *ptrFirst = NULL;
struct point *ptrLast = NULL;

void main()
{
	int choice =  0;
	while(1)
	{
		printf("1. Check if list is empty\n");
		printf("2. Print list\n");
		printf("3. Reset list\n");
		printf("4. Add point to beginning\n");
		printf("5. Add point to end\n");
		printf("6. Exit\n");
		
		scanf("%d", &choice);
		getchar();
		while(choice < 0 || choice >6)
		{
			scanf("%d", &choice);
			getchar();
		}
		
		switch(choice)
		{
			case 1: printf("%s", (isEmptyList(ptrFirst) == 0)? "Yes\n" : "No\n"); break;
			case 2: PrintList(ptrFirst); break;
			case 3: ResetList(ptrFirst, ptrLast); break;
			case 4: AddToBeginning(&ptrFirst, &ptrLast); break;
			case 5: AddToEnd(&ptrFirst, &ptrLast);break;
			case 6: ResetList(ptrFirst, ptrLast); return;
		}
	}
}

int isEmptyList(struct point *ptrF)
{
	return (ptrF == NULL)? 0: 1;
}

void PrintList(struct point *ptrF)
{
	struct point *ptrCur = ptrF;
	while(ptrCur != NULL)
	{
		printf("%d %d %s\n", ptrCur->x, ptrCur->y, ptrCur->label);
		ptrCur = ptrCur->ptrNext;
	}
}

void ResetList(struct point *ptrF, struct point *ptrL)
{
	struct point *ptrTemp = ptrF;
	while(ptrF != NULL)
	{
		ptrTemp = ptrF->ptrNext;
		free(ptrF);
		ptrF = ptrTemp;
	}
}

void AddToBeginning(struct point **ptrF, struct point **ptrL)
{
	struct point *ptrInput = (struct point *)malloc(sizeof(struct point));
	if(ptrInput == NULL)
	{
		printf("Fail to assign space!\n");
		return;
	}
	
	ptrInput->ptrNext = *ptrF;
	*ptrF = ptrInput;

	InputRecord(*ptrF);
}
void AddToEnd(struct point **ptrF, struct point **ptrL)
{
	struct point *ptrInput = (struct point *)malloc(sizeof(struct point));
	if(ptrInput == NULL)
	{
		printf("Fail to assign space!\n");
		return;
	}
	
	*ptrL->ptrNext = ptrInput;
	*ptrL = ptrInput;

	InputRecord(*ptrL);
}


void InputRecord(struct point *ptrNew)
{
	char buffer[20];
	
	printf("Input x: ");
	fgets(buffer, 20, stdin);
	ptrNew->x = atoi(buffer);
	
	printf("Input y: ");
	fgets(buffer, 20, stdin);
	ptrNew->y = atoi(buffer);
	
	printf("Input label: ");
	fgets(buffer, 20, stdin);
	strcpy(ptrNew->label, buffer);
}

[gerard4143]

Try replacing the problems line with this.

(*ptrL)->ptrNext = ptrInput;

[efronefron]

Try replacing the problems line with this.

(*ptrL)->ptrNext = ptrInput;

Thank you very much!! fixes the problem