[c] Why am I getting "void value not ignored as it ought to be"?

I have the following function :

void getdata(int arr[], int n)
{

    for (int i = 0; i < n; i++) 
    {
        int a = srand(time(NULL));
        arr[i] = a;
    }
}

And I call it in main:

getdata(arr, 1024);

I get "void value not ignored as it ought to be" but I don't understand what is wrong.Why do I get this error?

  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 you're using the value it returns (???) to assign, by initialization, to a.

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);
    /* ... */
}

"void value not ignored as it ought to be" this error occurs when function like srand(time(NULL)) does not return something and you are treating it as it is returning something. As in case of pop() function in queue ,if you will store the popped element in a variable you will get the same error because it does not return anything.

srand doesn't return anything so you can't initialize a with its return value because, well, because it doesn't return a value. Did you mean to call rand as well?

    int a = srand(time(NULL))
        arr[i] = a;

Should be

        arr[i] = rand();

And put srand(time(NULL)) somewhere at the very beginning of your program.

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

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 aren't allowed to assign void to integers, or any other type.

In the OP's 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, it's important that this thread gives a succinct, clear, and easily findable result.