Thread: Compiler Warnings in little multithread program

Hey,

as an experiment and an exercise I try to create a program which does two things at the same time:

The first thread shall wait for users input an override an int array.
The other thread shall constantly sum up the values every 30s.

Code:

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>


void job(int nums[]){
    while(1){
        int sum = 0;
        int length = (int)(sizeof(nums)/sizeof(nums[0])); //Compiler Warning Here
        for(int i = 0; i < length; i++){
            sum += nums[i];
        }
        printf("Length is %d", sum/length);
        sleep(30); //Compiler Warning here
    }


}
int main(int argc,char **argv){
    pthread_t *calc;
    int counter = 0;
    int nums[20];
    pthread_create(calc, NULL, *job, &nums); //Compiler Warning here
    while(1){
        char buf[50];
        fgets(buf, 50, stdin);
        nums[counter++%20] = strtol(buf, NULL ,10);
    }
    printf("Unreachable code");


}

Unfortunately this does not run properly.
I am explicty wondering about the first warning and the third.

Solution:
The error was here:

Code:

pthread_t *calc;
    int counter = 0;
    int nums[20];
pthread_create(calc, NULL, *job, &nums); //Compiler Warning here

Thread closed

There are a number of errors in your code. The following "works", except that without using a mutex it is not safe to modify the array in one thread when the other thread is also accessing it.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
 
#define ARRAY_SIZE 10
#define SECONDS_TO_SLEEP 5
 
void *job(void *data) {
    int *nums = data;
    while (1) {
        int sum = 0;
        for (int i = 0; i < ARRAY_SIZE; i++)
            sum += nums[i];
        printf("average: %.2f\n", (double)sum / ARRAY_SIZE);
        sleep(SECONDS_TO_SLEEP);
    }
    return NULL;
}
 
int main() {
    int nums[ARRAY_SIZE] = {0};
 
    pthread_t calc;
    if (pthread_create(&calc, NULL, job, nums) != 0) {
        fprintf(stderr, "Error: pthread_create\n");
        exit(EXIT_FAILURE);
    }
 
    for (int i = 0; ; ) {
        char buf[50];
        fgets(buf, sizeof buf, stdin);
        nums[i++ % ARRAY_SIZE] = atoi(buf);
    }
 
    return 0;
}