multiple POSIX threads

Question

I have a homework problem that I am currently stuck on. The parameters of the problem are as follows. 1.) It must accept a total of 5 integers from a user.

2.) It must have three threads, each of which performs a different function (Average, Minimum, and Maximum).

The problem that I am having is in declaring a global array empty array of 5 elements, and then modifying these elements. Each time I end up with a segfault, telling me that I am doing it incorrectly. The language, by the way, is C, emphatically not C++ (I'm not allowed to use it). If anyone can help me understand what is wrong, I would greatly appreciate it. Also, if it is a duplicate (I looked, nothing I saw addresses these problems), please point me to the question or article where it is addressed Thank you.

Code:

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

void *avgWorker(int in[]);
void *minWorker(int in[]);
void *maxWorker(int in[]);

int main(void)
{
  int it, *input;

  int in[5];

  pthread_t tid1,tid2,tid3;
  pthread_attr_t attr1, attr2,attr3;

  for (it = 0; it < 5; ++it)
    {
      printf("Please enter number %d of 5\n", (it + 1));

      input[it] = scanf("%d");
    }

  pthread_attr_init(&attr1);
  pthread_attr_init(&attr2);
  pthread_attr_init(&attr3);

  pthread_create(&tid1, &attr1, avgWorker(in), NULL);
  pthread_create(&tid2, &attr2, minWorker(in), NULL);
  pthread_create(&tid3, &attr3, maxWorker(in), NULL);

  pthread_join(tid1,NULL);
  pthread_join(tid2,NULL);
  pthread_join(tid3,NULL);

  return 0;
}

void *avgWorker(int in[])
{
  int total, avg, it;

  total = 0;

  for (it = 0; it < 5; ++it)
    {
      total += in[it];
    }

  avg = 0;

  avg = total / 5;

  printf("\n The average value is: %d. \n", avg);
}

void *minWorker(int in[])
{
  int min, it;
  min = 99999;

  for (it = 0; it < 5; ++it)
    {
      if (in[it] < min)
    min = in[it];
    }

  printf("The minimum value is: %d\n", min);
}

void *maxWorker(int in[])
{
  int max, it;

  max = -99999;

  for (it = 0; it < 5; ++it)
    {
      if (in[it] > max)
    max = in[it];
    }

   printf("The maximum value is: %d \n", max);
}

Finally, I am compiling this code using gcc, and using the -lpthread flag. Thanks again for any help that can be offered.

Answer 1

Your problem is in the line

input[it] = scanf("%d");

Look up the syntax of scanf... you need to provide the address where data is stored, so

scanf("%d", input+it);

should be an improvement. Or - as pointed out by @dreamlax, for more readable code

scanf("%d", &input[it]);

Answer 2

This is where it should crash:

input[it] = scanf("%d");

scanf returns number of fields read, not the data read. Addresses of variables where to store data into should be passed as parameters. Like this:

scanf("%d", &input[it]);

Also input is just an uninitialized pointer. It's not pointing anywhere (meaningful). I guess you wanted in, not input. You don't really need input variable at all.