diff --git a/ch05/exercise5_19.cpp b/ch05/exercise5_19.cpp
index 2b69b3d..81e4ae9 100644
--- a/ch05/exercise5_19.cpp
+++ b/ch05/exercise5_19.cpp
@@ -11,7 +11,7 @@ int main()
 		cout << "Input two strings: ";
 		string str1, str2;
 		cin >> str1 >> str2;
-		cout << (str1 <= str2 ? str1 : str2)
+		cout << (str1.size() <= str2.size() ? str1 : str2)
 			<< " is less than the other. " << "\n\n"
 			<< "More? Enter yes or no: ";
 		cin >> rsp;
diff --git a/ch06/README.md b/ch06/README.md
index c7502ee..d54d9da 100644
--- a/ch06/README.md
+++ b/ch06/README.md
@@ -189,7 +189,7 @@ bool is_empty(const string& s) { return s.empty(); }
 * (b) 名为 change_val 的函数，返回vector<int>的迭代器，有两个参数：一个是int，另一个是vector<int>的迭代器。
 
 ```cpp
-(a) bool compare(matrix &m1, matrix &m2);
+(a) bool compare(const matrix &m1, const matrix &m2);
 (b) vector<int>::iterator change_val(int, vector<int>::iterator);
 ```