Pthread doesn't work properly. c programming - c

Question

I'm trying to implement a mutex lock example code, but it doesn't work as well as the theory of mutex lock.
I create 10 threads for my program, 9 threads are reading an array and one thread change the array. In the theory of lock, if I lock the array before changing it then other threads can not read it.
but my program runs differently. please check the code below and help me to understand where to call pthread mutex lock functions:
// C program to generate random numbers
#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <time.h>
#include <stdlib.h>
#define NUM_THREADS 10
pthread_mutex_t lock;
int array[1000] = {0};
pthread_t threads[NUM_THREADS];
int change_array(int *array)
{
int arrayhelper[1000] = {0};
for (int i = 0; i < 1000; ++i)
arrayhelper[i] = i;
pthread_mutex_lock(&lock);
for (int i = 0; i < 1000; ++i)
array[i] = 0;
for (int i = 0; i < 1000; ++i)
array[i] = arrayhelper[i];
pthread_mutex_unlock(&lock);
return 1;
}
void *read_array(){
while(1)
if (array[10] == 0)
printf("%d failed to lock!\n", array[10]);
}
void *write_array(){
while(1)
{
sleep(1);
change_array(array);
}
}
int main (){
pthread_mutex_init(&lock, NULL);
for (int i = 0; i < 1000; ++i)
array[i] = i;
pthread_create(&threads[0], NULL, *write_array, NULL);
pthread_create(&threads[1], NULL, *read_array, NULL);
pthread_create(&threads[2], NULL, *read_array, NULL);
pthread_create(&threads[3], NULL, *read_array, NULL);
pthread_create(&threads[4], NULL, *read_array, NULL);
pthread_create(&threads[5], NULL, *read_array, NULL);
pthread_create(&threads[6], NULL, *read_array, NULL);
pthread_create(&threads[7], NULL, *read_array, NULL);
pthread_create(&threads[8], NULL, *read_array, NULL);
pthread_create(&threads[9], NULL, *read_array, NULL);
pthread_join(threads[0], NULL);
pthread_join(threads[1], NULL);
pthread_join(threads[2], NULL);
pthread_join(threads[3], NULL);
pthread_join(threads[4], NULL);
pthread_join(threads[5], NULL);
pthread_join(threads[6], NULL);
pthread_join(threads[7], NULL);
pthread_join(threads[8], NULL);
pthread_join(threads[9], NULL);
pthread_mutex_destroy(&lock);
pthread_exit(NULL);
return 1;
}
Theoretically, when you run this code, the read_array function should not print anything but in a moment array elements will be 0 and other threads achieve that.