diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..77a4663
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,8 @@
+files = add div mean mul sub sum
+
+all: $(files)
+
+$(files): %: %.c
+
+clean:
+	rm -v $(files) 
diff --git a/add.c b/add.c
index 1c4076e..4815fb2 100644
--- a/add.c
+++ b/add.c
@@ -13,10 +13,10 @@ int main(int argc, char **argv) {
   e1 = sscanf(argv[1], "%i", &v1);
   e2 = sscanf(argv[2], "%i", &v2);
   if(e1==EOF) {
-    eprintf("%s: argument %d cannot be parsed as int", *argv);
+    eprintf("%s: argument 1 cannot be parsed as int", *argv);
     return 1;
   } else if(e2==EOF) {
-        eprintf("%s: argument %d cannot be parsed as int", *argv);
+        eprintf("%s: argument 2 cannot be parsed as int", *argv);
     return 1;
   }
   out=v1+v2;
diff --git a/div.c b/div.c
index c7370a9..bb279fe 100644
--- a/div.c
+++ b/div.c
@@ -13,10 +13,10 @@ int main(int argc, char **argv) {
   e1 = sscanf(argv[1], "%i", &v1);
   e2 = sscanf(argv[2], "%i", &v2);
   if(e1==EOF) {
-    eprintf("%s: argument %d cannot be parsed as int", *argv);
+    eprintf("%s: argument 1 cannot be parsed as int", *argv);
     return 1;
   } else if(e2==EOF) {
-        eprintf("%s: argument %d cannot be parsed as int", *argv);
+        eprintf("%s: argument 2 cannot be parsed as int", *argv);
     return 1;
   }
   out=v1/v2;
diff --git a/mul.c b/mul.c
index bbe5733..b16bbf8 100644
--- a/mul.c
+++ b/mul.c
@@ -13,10 +13,10 @@ int main(int argc, char **argv) {
   e1 = sscanf(argv[1], "%i", &v1);
   e2 = sscanf(argv[2], "%i", &v2);
   if(e1==EOF) {
-    eprintf("%s: argument %d cannot be parsed as int", *argv);
+    eprintf("%s: argument 1 cannot be parsed as int", *argv);
     return 1;
   } else if(e2==EOF) {
-        eprintf("%s: argument %d cannot be parsed as int", *argv);
+        eprintf("%s: argument 2 cannot be parsed as int", *argv);
     return 1;
   }
   out=v1*v2;
diff --git a/sub.c b/sub.c
index e08bc46..02ba651 100644
--- a/sub.c
+++ b/sub.c
@@ -13,10 +13,10 @@ int main(int argc, char **argv) {
   e1 = sscanf(argv[1], "%i", &v1);
   e2 = sscanf(argv[2], "%i", &v2);
   if(e1==EOF) {
-    eprintf("%s: argument %d cannot be parsed as int", *argv);
+    eprintf("%s: argument 1 cannot be parsed as int", *argv);
     return 1;
   } else if(e2==EOF) {
-        eprintf("%s: argument %d cannot be parsed as int", *argv);
+        eprintf("%s: argument 2 cannot be parsed as int", *argv);
     return 1;
   }
   out=v1-v2;