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:

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#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;
}

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i have tried

Code:

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

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i have also tried saying

Code:

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

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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:

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

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I think you should write your loop like this instead:

Code:

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

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

thank you!