c – Why am I getting void value not ignored as it ought to be?

  int a = srand(time(NULL));

The prototype for srand is void srand(unsigned int) (provided you included <stdlib.h>).
This means it returns nothing … but youre using the value it returns (???) to assign, by initialization, to a.

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Edit: this is what you need to do:

#include <stdlib.h> /* srand(), rand() */
#include <time.h>   /* time() */

#define ARRAY_SIZE 1024

void getdata(int arr[], int n)
{
    for (int i = 0; i < n; i++)
    {
        arr[i] = rand();
    }
}

int main(void)
{
    int arr[ARRAY_SIZE];
    srand(time(0));
    getdata(arr, ARRAY_SIZE);
    /* ... */
}

The original poster is quoting a GCC compiler error message, but even by reading this thread, its not clear that the error message is properly addressed – except by @pmgs answer. (+1, btw)

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error: void value not ignored as it ought to be

This is a GCC error message that means the return-value of a function is void, but that you are trying to assign it to a non-void variable.

Example:

void myFunction()
{
   //...stuff...
}

int main()
{
   int myInt = myFunction(); //Compile error!

    return 0;
}

You arent allowed to assign void to integers, or any other type.

In the OPs situation:

int a = srand(time(NULL));

…is not allowed. srand(), according to the documentation, returns void.

This question is a duplicate of:

• error: void value not ignored as it ought to be
• void value not ignored as it ought to be – Qt/C++
• GCC C compile error, void value not ignored as it ought to be

I am responding, despite it being duplicates, because this is the top result on Google for this error message. Because this thread is the top result, its important that this thread gives a succinct, clear, and easily findable result.

c – Why am I getting void value not ignored as it ought to be?

srand doesnt return anything so you cant initialize a with its return value because, well, because it doesnt return a value. Did you mean to call rand as well?