update book code

eBook/exercises/chapter_12/hash_md5.go

@@ -0,0 +1,20 @@
+// hash_md5.go
+package main  
+  
+import (  
+       "fmt";  
+       "crypto/md5"  
+       "io"  
+)  
+  
+func main() {  
+     hasher := md5.New()
+	 b := []byte{}  
+     io.WriteString(hasher, "test")  
+     fmt.Printf("Result: %x\n", hasher.Sum(b)) 
+ 	 fmt.Printf("Result: %d\n", hasher.Sum(b))
+} 
+/* Output:
+Result: 098f6bcd4621d373cade4e832627b4f6
+Result: [9 143 107 205 70 33 211 115 202 222 78 131 38 39 180 246]
+*/