added (char *) casts
diff --git a/progs/demos/fire.c b/progs/demos/fire.c
index a648a9d..5c467ac 100644
--- a/progs/demos/fire.c
+++ b/progs/demos/fire.c
@@ -660,7 +660,7 @@
 
       if ((gluerr = gluBuild2DMipmaps(GL_TEXTURE_2D, 4, 128, 128, GL_RGBA,
 				      GL_UNSIGNED_BYTE, (GLvoid *) (tex)))) {
-	 fprintf(stderr, "GLULib%s\n", gluErrorString(gluerr));
+	 fprintf(stderr, "GLULib%s\n", (char *) gluErrorString(gluerr));
 	 exit(-1);
       }
    }
diff --git a/progs/demos/ipers.c b/progs/demos/ipers.c
index 87d70ef..8168034 100644
--- a/progs/demos/ipers.c
+++ b/progs/demos/ipers.c
@@ -186,7 +186,7 @@
        (gluerr =
 	gluBuild2DMipmaps(GL_TEXTURE_2D, 3, TEX_SKY_WIDTH, TEX_SKY_HEIGHT,
 			  GL_RGB, GL_UNSIGNED_BYTE, (GLvoid *) (tsky)))) {
-      fprintf(stderr, "GLULib%s\n", gluErrorString(gluerr));
+      fprintf(stderr, "GLULib%s\n", (char *) gluErrorString(gluerr));
       exit(-1);
    }
 
diff --git a/progs/demos/terrain.c b/progs/demos/terrain.c
index da5b90d..9063c93 100644
--- a/progs/demos/terrain.c
+++ b/progs/demos/terrain.c
@@ -572,7 +572,7 @@
    if ((gluerr = gluBuild2DMipmaps(GL_TEXTURE_2D, 1, 256, 256, GL_LUMINANCE,
 				   GL_UNSIGNED_BYTE,
 				   (GLvoid *) (&terrainpic[0])))) {
-      fprintf(stderr, "GLULib%s\n", gluErrorString(gluerr));
+      fprintf(stderr, "GLULib%s\n", (char *) gluErrorString(gluerr));
       exit(-1);
    }