Update printhex.en.md

subjects/printhex.en.md

@@ -5,6 +5,7 @@
 Write a program that takes a positive (or zero) number expressed in base 10, and displays it in base 16 (with lowercase letters) followed by a newline (`'\n'`).
 
 -   If the number of parameters is different from 1, the program displays a newline.
+-   Error cases have to be handled as shown in the example below. 
 
 ### Usage
 
@@ -16,7 +17,9 @@ student@ubuntu:~/piscine-go/test$ ./test "255"
 ff
 student@ubuntu:~/piscine-go/test$ ./test "5156454"
 4eae66
-student@ubuntu:~/piscine-go/test$
+student@ubuntu:~/piscine-go/test$ ./test
 
-student@ubuntu:~/piscine-go/
+student@ubuntu:~/piscine-go/test$ ./test "123 132 1" | cat -e
+0$
+student@ubuntu:~/piscine-go/test$ 
 ```