malloc and free on a Stack in C - c

Question

I'm trying to write a code that dynamically writes the Coordinates of a Point on the Stack and prints (and frees) them back:
#include <stdio.h>
#include <stdlib.h>
struct point{
float x;
float y;
float z;
}; typedef struct point POINT;
struct stackPoint{
POINT myPoint;
struct stackPoint *next;
}; typedef struct stackPoint STACKPOINT;
static STACKPOINT *stacktop = NULL;
void printStackElement(POINT aPoint){
printf(" x:%f \t y:%f \t z:%f\n", aPoint.x, aPoint.y, aPoint.z );
}
void push(POINT pushPoint){
STACKPOINT *newElem = malloc(sizeof(STACKPOINT));
stacktop = stacktop +1;
newElem->myPoint = pushPoint;
stacktop = newElem;
}
POINT pop(){
POINT b = stacktop->myPoint;
free(stacktop);
stacktop = stacktop -1;
return b;
}
int isEmpty(){
if(stacktop == NULL){
return 1;
}
return 0;
}
POINT readPoint(){
POINT a;
printf("Please enter your x-Coordinate: ");
scanf(" %f", &a.x);
printf("Please enter your y-Coordinate: ");
scanf(" %f", &a.y);
printf("Please enter your z-Coordinate: ");
scanf(" %f", &a.z);
return a;
}
int main(){
char quit = 0;
while(quit !=1 ){
printf("\n\n enter 'p' to enter another Point or 'q' to quit: " );
scanf(" %s", &quit);
switch(quit){
case 'p':
push(readPoint());
break;
case 'q':
quit = 1;
break;
default:
break;
}
}
while(isEmpty() == 0){
printStackElement(pop());
}
}
It prints the last entry but before printing the second to last entry, just an error message appears, that the "pointer beeing freed was not allocated".
I tried running it without the free() command, but then it just prints the first line and infite lines of just 0's
I also tried using the *stackTop pointer as a non static pointer instead of the *newElem pointer but that also didnt work..

Answer 1

It is supposed to be a linked list. Our professor just gave us this exercise and never even mentioned a linked list in any way or form.. Thank you very much, it works now!
I changed the push function to:
STACKPOINT *newElem = malloc(sizeof(STACKPOINT));
newElem->myPoint = pushPoint;
newElem->next = stacktop;
stacktop = newElem;
and the pop function to:
POINT b = stacktop->myPoint;
free(stacktop);
stacktop = stacktop->next;
return b;