diff --git a/21st_century_c/chapter11/Makefile b/21st_century_c/chapter11/Makefile
index 662fbfd..afd770f 100644
--- a/21st_century_c/chapter11/Makefile
+++ b/21st_century_c/chapter11/Makefile
@@ -1,4 +1,7 @@
-CFLAGS = -Wall -O0 --std=c11 -g -lm
+CFLAGS = -Wall -Wextra --std=c11 -g -lm -ftest-coverage -fprofile-arcs
+
+.PHONY : all
+all : simple_cplx seamlessone seamlesstwo dict_use
 
 
 simple_cplx : cplx.h complex.c simple_cplx.c
@@ -10,13 +13,10 @@ seamlessone : seamlessone.c
 seamlesstwo : seamlesstwo.c
 	$(CC) $(CFLAGS) -fms-extensions -Wno-microsoft $@.c -o $@
 
-dict_use : keyval.h keyval.c dict.h dict.c dict_use.c
-	$(CC) $(CFLAGS) keyval.c dict.c $@.c -o $@
+dict_use : memory.h memory.c keyval.h keyval.c dict.h dict.c dict_use.c
+	$(CC) $(CFLAGS) memory.c keyval.c dict.c $@.c -o $@
 
 
-.PHONY : all
-all : simple_cplx seamlessone seamlesstwo dict_use
-
 .PHONY : check
 check : *.h *.c
 	cppcheck --enable=warning --enable=style *.c
@@ -28,3 +28,6 @@ clean :
 	rm -f seamlesstwo
 	rm -f dict_use
 	rm -rf *.dSYM
+	rm -rf *.gcno
+	rm -rf *.gcda
+	rm -rf *.gcov
diff --git a/21st_century_c/chapter11/dict.c b/21st_century_c/chapter11/dict.c
index cd912d3..7e4512b 100644
--- a/21st_century_c/chapter11/dict.c
+++ b/21st_century_c/chapter11/dict.c
@@ -1,5 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
+
+#include "memory.h"
 #include "dict.h"
 
 
@@ -14,12 +16,11 @@ dictionary *dictionary_new(void) {
     dictionary_not_found = &dnf;
   }
   dictionary *out = malloc(sizeof(dictionary));
-  if(out != NULL) {
-    *out = (dictionary) {};
-  } else {
+  if(out == NULL) {
     fprintf(stderr, "Out of memory.\n");
     abort();
   }
+  *out = (dictionary) {};
   return out;
 
 }
@@ -29,14 +30,13 @@ static void dictionary_add_keyval(dictionary *in, keyval *kv) {
 
   in->length++;
   keyval **tmp = realloc(in->pairs, sizeof(keyval*) * in->length);
-  if(tmp != NULL) {
-    in->pairs = tmp;
-    tmp = NULL;
-    in->pairs[in->length-1] = kv;
-  } else {
+  if(tmp == NULL) {
     fprintf(stderr, "Out of memory.\n");
     abort();
   }
+  in->pairs = tmp;
+  tmp = NULL;
+  in->pairs[in->length-1] = kv;
 
 }
 
@@ -47,7 +47,11 @@ void dictionary_add(dictionary *in, char *key, void *value) {
     fprintf(stderr, "NULL is not a valid key.\n");
     abort();
   }
-  dictionary_add_keyval(in, keyval_new(key, value));
+  if(dictionary_find(in, key) == dictionary_not_found) {
+    dictionary_add_keyval(in, keyval_new(key, value));
+  } else {
+    printf("Key '%s' already exists!\n", key);
+  }
 
 }
 
@@ -80,8 +84,8 @@ void dictionary_free(dictionary *in) {
   for (size_t i = 0; i < in->length; i++) {
     keyval_free(in->pairs[i]);
   }
-  free(in->pairs);
-  free(in);
+  safeFree(in->pairs);
+  safeFree(in);
 
 }
 
diff --git a/21st_century_c/chapter11/dict_use.c b/21st_century_c/chapter11/dict_use.c
index 27e52f5..38b2ac2 100644
--- a/21st_century_c/chapter11/dict_use.c
+++ b/21st_century_c/chapter11/dict_use.c
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include "dict.h"
+#include "memory.h"
 
 
 
@@ -13,11 +14,21 @@ int main() {
 
   dictionary_add(d, "an int", &zero);
   dictionary_add(d, "a float", &one);
-  dictionary_add(d, "a string", &two);
+  for (size_t i = 0; i < 10; i++) {
+    dictionary_add(d, "a string", &two);
+  }
 
   printf("The integer I recorded was: %i\n", *(int*) dictionary_find(d, "an int"));
   printf("The string I recorded was: %s\n", (char*) dictionary_find(d, "a string"));
 
+  dictionary *new_d = dictionary_copy(d);
+
   dictionary_free(d);
 
-}
\ No newline at end of file
+  unsigned int three = 3;
+
+  dictionary_add(new_d, "an uint", &three);
+
+  dictionary_free(new_d);
+
+}
diff --git a/21st_century_c/chapter11/keyval.c b/21st_century_c/chapter11/keyval.c
index e0cb246..927a5d6 100644
--- a/21st_century_c/chapter11/keyval.c
+++ b/21st_century_c/chapter11/keyval.c
@@ -1,6 +1,8 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <strings.h>
+
+#include "memory.h"
 #include "keyval.h"
 
 
@@ -10,12 +12,11 @@ Create a new key/value pair.
 */
 keyval *keyval_new(char *key, void *value) {
   keyval *out = malloc(sizeof(keyval));
-  if(out != NULL) {
-    *out = (keyval){.key = key, .value = value};
-  } else {
+  if (out == NULL) {
     fprintf(stderr, "Out of memory.\n");
     abort();
   }
+  *out = (keyval){.key = key, .value = value};
   return out;
 }
 
@@ -25,12 +26,11 @@ the values in the old pair, not copies of their data.
 */
 keyval *keyval_copy(const keyval *in) {
   keyval *out = malloc(sizeof(keyval));
-  if(out != NULL) {
-    *out = *in;
-  } else {
+  if (out == NULL) {
     fprintf(stderr, "Out of memory.\n");
     abort();
   }
+  *out = *in;
   return out;
 }
 
@@ -39,9 +39,7 @@ keyval *keyval_copy(const keyval *in) {
 Free a existing key/value pair.
 */
 void keyval_free(keyval *in) {
-  if(in != NULL) {
-    free(in);
-  }
+  safeFree(in);
 }
 
 
@@ -49,5 +47,5 @@ void keyval_free(keyval *in) {
 Check if key of key/value pair matches given key.
 */
 int keyval_matches(const keyval *in, const char *key) {
-  return !strcasecmp(in->key, key);
+  return !strcmp(in->key, key);
 }
diff --git a/21st_century_c/chapter11/memory.c b/21st_century_c/chapter11/memory.c
new file mode 100644
index 0000000..695b258
--- /dev/null
+++ b/21st_century_c/chapter11/memory.c
@@ -0,0 +1,10 @@
+#include <stdlib.h>
+
+
+
+void saferFree(void **p) {
+  if (p != NULL && *p != NULL) {
+    free(*p);
+    p = NULL;
+  }
+}
diff --git a/21st_century_c/chapter11/memory.h b/21st_century_c/chapter11/memory.h
new file mode 100644
index 0000000..3e1f5cd
--- /dev/null
+++ b/21st_century_c/chapter11/memory.h
@@ -0,0 +1,3 @@
+void saferFree(void **p);
+
+#define safeFree(p) saferFree((void **) &(p));
diff --git a/21st_century_c/chapter11/seamlesstwo.c b/21st_century_c/chapter11/seamlesstwo.c
index 408b967..f7d3173 100644
--- a/21st_century_c/chapter11/seamlesstwo.c
+++ b/21st_century_c/chapter11/seamlesstwo.c
@@ -38,4 +38,4 @@ int main() {
   double xylength = length(p.p2);
   printf("Its projection onto the XY plane is %g units from the origin\n", xylength);
 
-}
\ No newline at end of file
+}
diff --git a/21st_century_c/chapter11/simple_cplx.c b/21st_century_c/chapter11/simple_cplx.c
index a478833..cf08f89 100644
--- a/21st_century_c/chapter11/simple_cplx.c
+++ b/21st_century_c/chapter11/simple_cplx.c
@@ -5,7 +5,7 @@
 
 int main() {
 
-  int complex a = 1 + 2I;
+  complex int a = 1 + 2I;
   complex double b = 2 + I;
   gsl_complex c = gsl_cplx_from_c99(a);
 
@@ -28,4 +28,4 @@ int main() {
   printf("v dot (1+2i) again\n");
   gsl_vector_complex_print(dot(v, c));
 
-}
\ No newline at end of file
+}