#include <stdio.h>
#include <stdlib.h>

struct binop { struct exp * e1, * e2; };
union node {  int value; struct binop b; };
struct exp { char tag; union node n; };

struct exp * newInt(int i)
{  struct exp * e;
   e = (struct exp *)malloc(sizeof(struct exp));
   e->tag = 'I';
   e->n.value = i;
   return e;
}

struct exp * newBinop(char op,struct exp * e1,struct exp * e2)
{  struct exp * e;
   e = (struct exp *)malloc(sizeof(struct exp));
   e->tag = op;
   e->n.b.e1 = e1;
   e->n.b.e2 = e2;
   return e;
}

printTree(struct exp * e,int depth)
{  int i;
   for(i=0;i<depth;i++)
    printf(" ");
   switch(e->tag)
   {  case 'I': printf("%d\n",e->n.value);
                return;
      default: printf("%c\n",e->tag);
               printTree(e->n.b.e1,depth+1);
               printTree(e->n.b.e2,depth+1);
   }
}

main(int argc,char ** argv)
{  struct exp * e;
   e = newBinop('*',newBinop('+',newInt(1),newInt(2)),
                    newBinop('-',newInt(3),newInt(4)));
   printTree(e,0);
}