Infinite loop on BFS - c

Question

I'm trying to make a program that finds if node B belongs to the subtree starting from node A. I wrote the code in C and self-implemented a mechanism for queue because I'm using BFS to traverse the tree. The problem is that my code runs into an infinite loop saying that my queue is full even is not.
Code:
#include <stdlib.h>
#include <stdio.h>
#define MAXSIZE 6
typedef struct Queue
{
int capacity;
int size;
int front;
int rear;
int * elements;
}Queue;
Queue * createQueue(int maxElements)
{
Queue *q;
if (NULL != (q = (Queue *)malloc(sizeof(Queue))))
{
q->elements = (int*)malloc(maxElements * sizeof(int));
q->size = 0;
q->capacity = maxElements;
q->front = 0;
q->rear = -1;
return q;
}
}
void dequeue(Queue *q)
{
if (0 == q->size)
{
printf("Queue is empty\n");
return;
}
else
{
q->size--;
q->front++;
if (q->front == q->capacity)
{
q->front = 0;
}
}
}
int front(Queue *q)
{
if (q->size == 0)
{
printf("queue is empty\n");
exit(0);
}
return q->elements[q->front];
}
void enqueue(Queue *q, int element)
{
if (q->size == q->capacity)
{
printf("queue is full \n");
}
else
{
q->size++;
q->rear++;
if (q->rear == q->capacity)
{
q->rear = 0;
}
q->elements[q->rear] = element;
}
return;
}
void readInput(int A[],int B[],int M[][MAXSIZE],int N)
{
FILE * fp;
int row, col;
for (int i = 0; i < 5; i++)
for (int j = 0; j < 5; j++)
M[i][j] = 0;
if (0 == fopen_s(&fp,"input.txt", "r"))
{
fscanf_s(fp, "%d", &N);
for (int i = 0; i < N; i++)
fscanf_s(fp,"%d ", &A[i]);
for (int i = 0; i < N; i++)
fscanf_s(fp,"%d ", &B[i]);
for (int i = 0; i < N; i++)
{
fscanf_s(fp, "%d %d", &row,&col);
M[row][col] = 1;
}
}
}
bool vBelongsToUSubtree(int M[][MAXSIZE], int *u, int* v)
{
bool belongs = false, visited[MAXSIZE];
for (short i = 0; i < MAXSIZE; i++)visited[i] = false;
visited[*u] = true;
Queue *q = createQueue(MAXSIZE);
enqueue(q, *u);
printf("%d\n", front(q));
int node;
while (0 != q->size)
{
node = front(q);
dequeue(q);
for (int i = 1; i < MAXSIZE; i++)
{
if (1 == M[node][i] and false == visited[i])
{
enqueue(q, node);
visited[node] = true;
if (node == *v)return true;
}
//printf("!\n");
}
//printf("%d\n", node);
}
/*for (int i = 0; i < q->size; i++)
{
printf("%d \n", front(q));
}
*/
return belongs;
}
int main()
{
int A[100], B[100], M[MAXSIZE][MAXSIZE], N=0;
readInput(A, B, M, N);
for(int i=1;i<=MAXSIZE;i++)
for(int j=i;j<=MAXSIZE;j++)
if(vBelongsToUSubtree(M, &i, &j))printf("yes");
else printf("not");
system("pause");
return 0;
}

Answer 1

As pointed out in the comments, there are several problems with your existing code. Before it is expected to work at all, you should address them.
This answer addresses only the infinite loop you asked about...
Also pointed out in the comments:
If i or j in the statement: if(vBelongsToUSubtree(M, &i, &j))printf("yes"); are not controlled properly they may never satisfy the exit condition in for(int i=1;i<=MAXSIZE;i++) or for(int j=i;j<=MAXSIZE;j++)
Following i through to the end of its execution flow, it appears it (and perhaps j) are never changed.
The chain of calls passing i :
if(vBelongsToUSubtree(M, &i, &j))printf("yes");
Which in turn calls:
enqueue(q, *u);
Which has the prototype:
void enqueue(Queue *q, int element)
where int element is the value for i, and is not changed. (nor could it be using this prototype.)