Fixed a few additional header file issues in examples

src/examples/ex17.c

@@ -19,6 +19,9 @@
    Description:    This code solves an "NDIM-D Laplacian" using CG.
 */
 
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <math.h>
 #include "HYPRE_struct_ls.h"
 

src/examples/ex18.c

@@ -19,6 +19,9 @@
    Description:    This code solves an "NDIM-D Laplacian" using CG.
 */
 
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <math.h>
 #include "HYPRE_sstruct_ls.h"
 

src/examples/ex18comp.c

@@ -20,6 +20,9 @@
 */
 
 #include <complex.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <math.h>
 #include "HYPRE_sstruct_ls.h"