Newb Question: scanf() in C

Question

So I started learning C today, and as an exercise i was told to write a program that asks the user for numbers until they type a 0, then adds the even ones and the odd ones together. Here is is (don't laugh at my bad style):

#include <stdio.h>;

int main() {
    int esum = 0, osum = 0;
    int n, mod;

    puts("Please enter some numbers, 0 to terminate:");
    scanf("%d", &n);

    while (n != 0) {
        mod = n % 2;
        switch(mod) {
        case 0:
            esum += n;
            break;
        case 1:
            osum += n;
        }
        scanf("%d", &n);
    }
    printf("The sum of evens:%d,\t The sum of odds:%d", esum, osum);
    return 0;
}

My question concerns the mechanics of the scanf() function. It seems that when you enter several numbers at once separated by spaces (eg. 1 22 34 2 8), the scanf() function somehow remembers each distinct numbers in the line, and steps through the while loop for each one respectively. Why/how does this happen?

Example interaction within command prompt:

-> Please enter some numbers, 0 to terminate:
42 8 77 23 11 (enter)
0 (enter)
-> The sum of evens:50, The sum of odds:111

I'm running the program through the command prompt, it's compiled for win32 platforms with visual studio.

Answer 1

It happens because scanf function gets its input from the standard input stream. It is called stream for a reason: everything you enter is put into that stream, and scanf reads that stream. Whatever you put into the input stream will stay there until something like scanf gets it out of there.

In other words, scanf doesn't really "remember" anything. It is the input stream that does all the "remembering".

Answer 2

Notice that you're calling scanf() each time you go through the loop; each time you call scanf() with the arguments "%d" and &n, it reads a single integer into the variable n and advances to the position immediately after that integer in the input stream.

You can sort of think of the input stream as a "string" of sorts. Suppose I typed "25 16 0"; after scanf() reads the first integer, the input stream becomes "16 0"; if you call scanf() again, you'll read the integer 16 and the input string becomes "0".