how use EOF stdin in C

Question

I need to input coordinates into an array until EOF is encountered, but something is wrong in my code. I used ctrl+Z, ctrl+D

int main()
{
    int x[1000],y[1000];
    int n=0,nr=0,a,b,i;
    printf("Enter the coordinates:\n");
    while(scanf ( "%d %d ", &a, &b) == 2)
    {
     x[n]=a;
     y[n]=b;
     n++;
    }
    if (!feof(stdin))
    {
       printf("Wrong\n");
    }
    else
    {
       for(i=0;i<n;i++)
       printf("%d %d\n", x[i], y[i]);
    }

  return 0;
}

Answer 1

I suggest using

while(!feof(stdin) && scanf ( "%d %d ", &a, &b) == 2)

and actually it is better to test feof after (not before!) some input operation, so:

while (scanf("%d %d ", &a, &b) == 2 && !feof(stdin))

BTW, on many systems stdin is line buffered, at least with interactive terminals (but perhaps not when stdin is a pipe(7)), see setvbuf(3)

On Linux & POSIX you might consider reading every line with getline(3) (or even with readline(3) if reading from the terminal, since readline offers editing abilities), then parsing that line with e.g. sscanf(3) (perhaps also using %n) or strtol(3)

Answer 2

The only real problem that I see in your code is the extra spaces in the scanf format string. Those spaces tell scanf to consume whitespace character on the input, which makes scanf not return to your code until it hits a non-whitespace character (such as a letter, a number, punctuation, or EOF).

The result is that after typing two numbers and then Enter, you have to type Ctrl-D (Ctrl-Z in DOS/Windows) twice before your program escapes the while loop.