using threads for the first time - c

Question

//trying to make each thread print its thread number not id and then print a message from the array would like to be able to pass array in pthread create but right now I am getting a an error array subscript is not an integer please help me
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <pthread.h>
void * print_funtion( void* i, void* message)
{
printf("Thread %d: ",(int*) i);
printf("Thread %s: ", message);
return NULL;
}
int main(int argc, char* argv[]){
int i;
int num = atoi(argv[1]);
//printf("%d \n", num);
for(i = 1; i <= num; i++)
{
char *messages[] = {"Hello", "Bonjour", "Hola", "Shalom", "Namaste", "Gutan Tag", "God dag","Ola", "Salut", "Napot", "Dia"};
//printf("%d \n", i);
pthread_t tid;
pthread_create(&tid, NULL, print_funtion,(void*)i, (void*)messages[i]);
pthread_join(tid,NULL);
}
return 0;
}

Answer 1

There are many problems in the code and I'll point them out individually as comments:
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <pthread.h>
// Note: In most cases, you should use (char *) for strings instead of char[XX].
// Note: You don't need to set the number of elements in the array
// because it is automatically inferred from the initializer.
char *messages[] = {"Hello", "Bonjour", "Hola", "Shalom", "Namaste", "Gutan Tag", "God dag","Ola", "Salut", "Napot", "Dia"};
void *print_function(void *data)
{
// The data you passed is int not a pointer to int.
int i = (int)data;
printf("Thread %d: \n", i);
// You need to use %s for printing string.
printf("Message: %s\n", messages[i]);
return NULL;
}
int main(int argc, char* argv[])
{
int i;
int num = atoi(argv[1]);
// Limit the number of running threads so you don't slow down you computer (10 is already too much. It depends on the number of cores you CPU has).
#define MAX_NUM_OF_THREADS 10
if(num > MAX_NUM_OF_THREADS)
num = MAX_NUM_OF_THREADS;
// I explain why we need to store the thread ids down below.
pthread_t thread_ids[MAX_NUM_OF_THREADS];
for(i = 0; i < num; i++)
{
pthread_t tid;
void *thread_data = (void *)(i + 1);
pthread_create(&tid, NULL, print_function, thread_data);
thread_ids[i] = tid;
}
// You can't join with the thread in the previous loop because it will serialize thread creation.
// Meaning the program will not create the next thread before the current thread finish execution.
// Instead, you need to create all the threads first then you join to them one by one afterward.
// And for that you need to store the thread ids for each thread in order to join with them after they are created.
for(i = 0; i < num; i++)
{
pthread_join(thread_ids[i], NULL);
}
return 0;
}