Strange result

Hi, according to the previous question, I have done my program, but there are some strange results comes out. Please help.
Here are the code:
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#include <stdio.h>
#include <math.h>

typedef struct{
      double n;
      double d;
}fract;

fract add_fract(fract *f1, fract *f2);
fract subtract_fract(fract *f1, fract *f2);
fract multiply_fract(fract *f1, fract *f2);
fract divide_fract(fract *f1, fract *f2);

int main(void){
  fract f1, f2, f3_add, f3_subtract, f3_multiply, f3_divide;
 
  printf ("Numerator for f1: ");
  scanf ("%lf", &f1.n);
  printf ("Denorminator for f1: ");
  scanf ("%lf", &f1.d);

  printf ("Numerator for f2: ");
  scanf ("%lf", &f2.n);
  printf ("Denorminator for f2: ");
  scanf ("%lf", &f2.d);

  f3_add = add_fract(&f1, &f2);
  f3_subtract = subtract_fract(&f1, &f2);
  f3_multiply = multiply_fract(&f1, &f2);
  f3_divide = divide_fract(&f1, &f2);

  printf ("\nAdd = %d/%d\n", (int)f3_add.n, (int)f3_add.d);
  printf ("Subtract = %d/%d\n", (int)f3_subtract.n, (int)f3_subtract.d);
  printf ("Multiply = %d/%d\n", (int)f3_multiply.n, (int)f3_multiply.d);
  printf ("Divide = %d/%d\n", (int)f3_divide.n, (int)f3_divide.d);

  return (0);
}

fract add_fract(fract *f1, fract *f2){
  fract f;
  double common, gcd;

  if (f1->d != f2->d){
    common = f1->d * f2->d;      //Find the common denorminator

      f1->n = f1->n * f2->d;
      f2->n = f2->n * f1->d;

      (int)f.n = f1->n + f2->n;
      (int)f.d = common;

      gcd = euclid(&f.n, &f.d);
  }
  else{
    f.n = f1->n + f2->n;
      f.d = f1->d;

      gcd = euclid(&f.n, &f.d);
  }
  return f;
}

fract subtract_fract(fract *f1, fract *f2){
  fract f;
  double common, gcd;

  if (f1->d != f2->d){
    common = f1->d * f2->d;      //Find the common denorminator

      f1->n = f1->n * f2->d;
      f2->n = f2->n * f1->d;

      f.n = f1->n - f2->n;
      f.d = common;

      gcd = euclid(&f.n, &f.d);
  }
  else{
    f.n = f1->n + f2->n;
      f.d = f1->d;

      gcd = euclid(&f.n, &f.d);
  }
  return f;
}

fract multiply_fract(fract *f1, fract *f2){
  fract f;
  double gcd;

  f.n = f1->n * f2->n;
  f.d = f1->d * f2->d;

  gcd = euclid(&f.n, &f.d);

  return f;
}

fract divide_fract(fract *f1, fract *f2){
  fract f;
  double gcd;

  if (f1->d != 0 || f2->d != 0){
    f.n = f1->n * f2->d;
    f.d = f1->d * f2->n;

      gcd = euclid(&f.n, &f.d);
  }
  else printf ("Cannot divide by zero\n");
  return f;
}
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The output are as the following if I input 1/3 and 5/6

Add = 7/6
Subtract = -1/2
Multiply = 90/1
Divide = 8/5


THANKS !