/********************************************
*     Elementary operations on fractions    *
* ----------------------------------------- *
* This program allows user performing       *
* operations on fractions such as:          *
*         3/4 x 8/9 - 4/5                   *
*                                           *
* Sample run:                               *
*                                           *
* 3 4                                       *
* *                                         *
* 8 9                                       *
* +                                         *
* -4 5                                      *
* =                                         *
* Result is -2/15                           *
* ----------------------------------------- *
* Ref.: "Mathématiques par l'informatique   *
*        individuelle (1) par H. Lehning    *
*        et D. Jakubowicz, Masson, Paris,   *
*        1982" [BIBLI 06].                  *
*                                           *
*              C++ version by J-P Moreau.   *
*                  (www.jpmoreau.fr)        *
********************************************/
#include <stdio.h>
#include <math.h>

//Labels e10,e20,fin

      int b,g,h,p,q,r,s,t,u;
      char cs[2];

      void P300() {     // substract
        r=-r;
        p=p*s+q*r;
        q=q*s;          // common denominator for all operations
      }

      void P310() {     // add
        p=p*s+q*r;
        q=q*s;          // common denominator for all operations
      }

      void P330() {     // Divide
        b=r;
        r=s; s=b;
        p=p*r;
        q=q*s;          // common denominator for all operations
      }

      void P360() {     // Multiply
        p=p*r;
        q=q*s;          // common denominator for all operations
      }

      void P390() {     // simplify result
      //Labels: e10,e20
        t=p;
        u=q;
e11:    b=(int) (t-u*floor(t/u));
        if (b==0) goto e21;
        t=u; u=b;
        goto e11;
e21:    p=p / u; q=q / u;
		if (q<0) {q=-q; p=-p;}
      }


void main() {
  printf("\n");
//*** enter first fraction p/q (p=0 to exit) ***
e10:printf(" ? ");
  scanf("%d %d",&p,&q); 
  if (p==0 || q==0) goto fin;
//*** enter operator:
//     = to view current result p/q
//     s to save current result
//     +,-,*,/ arithmetic operator
//***
e20:printf(" ? ");
  scanf("%s",&cs[0]);
  if (cs[0]=='=') {printf(" Result is %d/%d\n",p,q); goto e20;} 
  if (cs[0]=='s') {g=p; h=q; goto e10;}
  if (cs[0]=='q') goto fin;
//*** enter next fraction r/s (if s=0, take current stored result) ***
  printf(" ? ");
  scanf("%d %d",&r,&s); 
  if (r==0) goto fin;
  if (s==0) {r=g; s=h;}
  // computing result
  if (cs[0]=='+') P310();
  if (cs[0]=='-') P300();
  if (cs[0]=='*') P360();
  if (cs[0]=='/') P330();
  P390();
  goto e20;
fin: ;
}


// end of file fraction.cpp