diff --git a/Week4.ipynb b/Week4.ipynb
index ba6a247..417f278 100644
--- a/Week4.ipynb
+++ b/Week4.ipynb
@@ -197,11 +197,11 @@
    "source": [
     "filenames = [\"program.c\", \"stdio.hpp\", \"sample.hpp\", \"a.out\", \"math.hpp\", \"hpp.out\"]\n",
     "newfilenames = []\n",
-    "for file in filenames:\n",
-    "  if '.hpp' in file:\n",
-    "    newfilenames.append((file,file[:-2]))\n",
+    "for file in range(len(filenames)):\n",
+    "  if 'hpp' in filenames[file][-3:]:\n",
+    "    newfilenames.append(filenames[st][:-2])\n",
     "  else:\n",
-    "    newfilenames.append((file,file))\n",
+    "    newfilenames.append(filenames[st])\n",
     "\n",
     "print (newfilenames) # Should be [('program.c', 'program.c'), ('stdio.hpp', 'stdio.h'), ('sample.hpp', 'sample.h'), ('a.out', 'a.out'), ('math.hpp', 'math.h'), ('hpp.out', 'hpp.out')]"
    ]