usage of the return value of scanf

Question

I am learning C from a book and I am starting with loop instructions. But there is a sample code which I could not understand.

Can anyone tell me why author has used status = scanf("%ld", &num); ? Why there is a = with scanf ?

/* summing.c -- sums integers entered interactively */
#include <stdio.h>
int main(void)
{
    long num;
    long sum = 0L; /* initialize sum to zero */
    int status;      
    printf("Please enter an integer to be summed ");
    printf("(q to quit): ");
    status = scanf("%ld", &num);
    while (status == 1) /* == means "is equal to" */
    {
        sum = sum + num;
        printf("Please enter next integer (q to quit): ");
        status = scanf("%ld", &num);
    }
    printf("Those integers sum to %ld.\n", sum);
    return 0;
}

Answer 1

Because scanf() returns a value indicating how well the string matched the format passed, i.e. how many parameters were successfuly filled with data.

You would know that if your read some kind of manual page, or the standard, if you ever encounter a function that you don't know, always read about it as much as you can, so you can understand how to use it.