SIGSEV error in Circular queue function in c - c

Question

Hey guys i have been trying to create circular queue library for my project purpose.But while developing a SIGEGV error from a if statement under empty function whenever i am using an condition at that particular if condition i am encountering this error.
#include <stdio.h>
#define SIZE 5
typedef struct queue
{
int values[SIZE];
int head;
int tail;
int size;
int count;
int full_flag;
}queue_t;
int init(queue_t* q)
{
//q->values;
q->head=-1;
q->tail=-1;
q->size=SIZE;
q->count=1;
q->full_flag=0;
}
int empty(queue_t* q) //This if statement where i am getting problem at
{
if(q->count==0)
{
return 1;
}
else
{
return 0;
}
}
int enqueue(queue_t* q,int input)
{
if(empty(q)==1)
{
printf("Queue is full\n");
}
else
{
if(q->head=-1)
{
q->head=0;
}
q->tail=(q->tail+1)%q->size;
q->values[q->tail]=input;
q->count++;
}
}
int deque(queue_t* q)
{
int result;
q->head=q->head%q->size;
result=q->values[q->head];
q->head++;
printf("Removing from %d\n",result);
q->count--;
}
int main(void) {
queue_t* q;
//q->head=5;
// q->values[2]=3;
init(q);
enqueue(q,2);
enqueue(q,3);
enqueue(q,4);
enqueue(q,5);
enqueue(q,6);
//printf("%d\n",q->values[q->tail]);
//printf("%d",q->head);
// your code goes here
return 0;
}
when i executing without that if loop everything works fine.BUt with it everything becoming a chaos.Please guys help me out thanks in advance

Answer 1

you have defined a pointer without allocating memory to it in your main function
queue_t* q;
this is a wild(dangling) pointer because it doesn't point to a specific piece of memory. you must allocate memory to it. like this:
queue_t* q = malloc(sizeof(queue_t));
or
queue_t q;
queue_t* pq = &q;