Segmentation Fault - Producer Consumer

This is my basic code , now the problem is that it runs for couple of loops and then gives segmentation fault. Now I know that segmentation error is due to illegal read/write at a memory location, but I haven't used any pointers on that note.

#include<stdio.h>
#include<math.h>
#include<stdbool.h>
#include<pthread.h>
#include<stdlib.h>

int counter = 0;
int BUFFER_SIZE = 5;
int buffer[] = {0};
int in = 0;
int out = 0;
void *prod(char);
void *cons(void);
bool flag = true;

void main()
{   int i, j;

    pthread_t thread1, thread2; 
    do{

            flag = true;
            i = pthread_create(&thread1, NULL, prod('i'), NULL);
            flag = true;
            j = pthread_create(&thread2, NULL, cons(), NULL);

    }while(1);
}

void* prod(char a)
{
    while (flag) {
      printf("\nCounter  = %d", counter);

while (counter == BUFFER_SIZE) {
      printf("\nBusy Waiting!!!");
} 

buffer[in] = a;
in = (in + 1) % BUFFER_SIZE;
printf("\nProducer produced an item %c!",a);
counter++;
printf("\nTotal items produced = %d",counter);

flag = false;

}
}

void* cons()
{
  char a;
  while (flag) {
    printf("\nCounter  = %d",counter);
    while (counter == 0){printf("\nBusy Waiting!!!");
  } 

  a = buffer[out];
  out = (out + 1) % BUFFER_SIZE;

  counter--;

  printf("\nTotal items remaining = %d",counter);
  flag = false;
}
}

OUPUT

Solution

You have multiple severe bugs:

You are creating threads in an eternal loop, until the program runs out of memory. What you want to do is to just create n threads once, then let the main program loop (forever?) after that.
pthread_create(&thread1, NULL, prod('i'), NULL) is incorrect, you are calling the callback function here instead of providing a function pointer to it. Arguments to the callback need to be passed separately. Read the manual about pthread_create.
pthreads expect a function format of the type void* func (void*). You are not allowed to use any other function format. So both of your callback functions have the wrong format.
You aren't using any form of protection mechanism for variables shared between multiple threads. You need to use a mutex or similar.
stdio.h is not necessarily thread-safe, depending on which system and C standard version you are using. See stdout thread-safe in C.