[C] error: expected expression before ‘{’

[and77]

Salve,compilando il codice che segue ottengo il seguente errore:
error: expected expression before ‘{’ token
Avete suggerimenti?Grazie.

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

void *prod_rtn(void *);
void *cons_rtn(void *);

struct data{
	int a;
	pthread_mutex_t mutex;
};

int main(){
	pthread_t prod;
	pthread_t cons;
	struct data *arg;
	int err;

	
	if( (arg=(struct data*)malloc(sizeof(struct data))) == NULL){
		perror("malloc() error");
		exit(1);
	}
	arg->a=0;
	arg->mutex=PTHREAD_MUTEX_INITIALIZER;


	if( (err=pthread_create(&prod,NULL,prod_rtn,(void*)arg)) != 0){
		printf("pthread_create() error %s\n",strerror(err));
		exit(1);
	}
	if( (err=pthread_create(&cons,NULL,cons_rtn,(void*)arg)) != 0){
		printf("pthread_create() error %s\n",strerror(err));
		exit(1);
	}

	while(1){
		if( arg->a > 10)
			break;
		else
			printf("Master thread %d\n",arg->a);
	}
}

void *prod_rtn( void* arg){
	int err;
	struct data *args=(struct data*)arg;

	if( (err=pthread_mutex_lock(&(args->mutex))) != 0){
		printf("pthread_mutex_lock() error %s\n",strerror(err));
		exit(1);
	}
	printf("PRODUTTORE\n");
	args->a=(args->a)+2;

	if( (err=pthread_mutex_unlock(&(args->mutex))) != 0){
		printf("pthread_mutex_lock() error %s\n",strerror(err));
		exit(1);
	}
}

void *cons_rtn( void* arg){
	int err;
	struct data *args=(struct data*)arg;

	if( (err=pthread_mutex_lock(&(args->mutex))) != 0){
		printf("pthread_mutex_lock() error %s\n",strerror(err));
		exit(1);
	}
	printf("CONSUMATORE\n");
	args->a=(args->a)+1;

	if( (err=pthread_mutex_unlock(&(args->mutex))) != 0){
		printf("pthread_mutex_lock() error %s\n",strerror(err));
		exit(1);
	}
}