help with EOF

hello, i am working on this program that calculates the resistance of an arbitrary number of floating points, the input needs to end when i press zero or EOF...i have the zero part but for some reason i can't get the EOF part....
here is my code

Code:

#include <stdio.h>
#define   SENTINAL   0

int main()
{
   
   double r1;
   double resistance = 0.0;

   printf("Enter the resistance or zero to end input:\n");
   
   while ( 1 )  {
      scanf("%lf", &r1);
      if ((r1 == SENTINAL))
         break; 
      resistance += (1/r1); 
}
   
   if (resistance == 0)
      printf("\nNo values entered.\n\n");
   else 
      printf("\nTotal resistance of the ciruit is %.3f ohms\n", 1/resistance);
      
   system("pause");
   return 0;
}

i have tried

Code:

if ((r1 == SENTINAL) || (r1 == EOF))
         break;

i have also tried saying

Code:

if (scanf("%lf", &r1) == EOF)
break;

the scanf code ends the input but it changes my numbers...can anyone give me any insight to what i am doing wrong? thanks

rl can never have the value EOF. scanf will return the value EOF. Since you need to check for both EOF and zero, then do so:

Code:

if (retval == EOF || inputval == 0)

I think you should write your loop like this instead:

Code:

while (scanf("%lf", &r1) == 1 && r1 != SENTINAL) {
    resistance += 1.0 / r1;
}

Incidentally, I think that SENTINAL should be SENTINEL, and you really should indent your code more consistently.

thank you!