add include <stdlib>

NN/stack.c

+#include <stdlib.h>
+
 	static struct node
 	{ int key; struct node *next; };
 	static struct node *head, *z, *t;

NN/stackpair.c

+#include <stdlib.h>
+
 	static struct node
 	{ int key; struct node *next; };
 	static struct node *heada, *za, *ta;
 	static struct node *headb, *zb, *tb;
+
         stackpairinit_() {stackpairinit();}
 	stackpairinit () 
 	   {
@@ -17,6 +20,7 @@
 	     zb->next = zb;
 	     zb->key = 0;
 	   }
+
         stackpairflush_() {stackpairflush();}
 	stackpairflush () 
 	   {
@@ -25,6 +29,7 @@
              free(za);
              free(zb);
 	   }
+
         pushpair_(pa, pb)  int *pa; int *pb; {pushpair(pa, pb);}
 	pushpair (pa, pb)
              int *pa;
@@ -42,6 +47,7 @@
 	     tb->key = vb; tb->next = headb->next;	
 	     headb->next =tb;	
 	   }
+
         poppair_(xa,xb)  int *xa; int *xb; {poppair(xa,xb);}
 	poppair (xa,xb)
              int *xa;
@@ -54,6 +60,7 @@
 	     *xb = tb->key;
 	     free(tb);
 	   }
+
         stackpairempty_(i) int *i; {stackpairempty(i);}
 	stackpairempty (i)
             int *i;