[C++] implémention d'un arbre binaire

#include<stdio.h>
#include<stdlib.h>
typedef struct noeud * tree;
struct noeud
{int val;
tree fg,fd;
};
tree cree_noeud(int val)
{
tree a;
a=(tree)malloc(sizeof(noeud));
if(!a)
{printf("pas d espace");
return(NULL);
}
if(a)
{
a->fd=NULL;
a->fg=NULL;
a->val=val;
printf("%d",a->val);
return(a);
}
}
tree ajout(tree b,tree a,tree r)
{a=r;
if(a==NULL)
{
return b;
}
else
{
if(b->val<a->val)
{
if(a->fd==NULL)
{
a->fd=b;
printf("%d",a->val);
return(r);
}
else
{
r=ajout(b,a->fd,r);
return(r);
}
}
else
{
if(a->fg==NULL)
{
a->fg=b;
printf("%d",a->val);
return r;
}
else
{
r=ajout(b,a->fg,r);
return(r);
}
}
}
}
void prefixe(tree a)
{
if(a!=NULL)
{
printf("%d ",a->val);
prefixe(a->fg);
prefixe(a->fd);
}
}

void main()
{int x,l,h;
tree r=NULL,b=NULL,k=NULL,a=NULL;free(r);
printf("donner un entier : \n" );
scanf("%d",&x);
b=cree_noeud(x);
r=ajout( b,a, r);
printf("%d",r->val);
flushall();
printf("donner un entier : \n");
scanf("%d",&x);
b=cree_noeud(x);
r=ajout( b,a, r);

prefixe(r);
}