fixed Mooophy/Cpp-Primer#172

ch06/README.md

@@ -37,24 +37,7 @@ int main()
 }
 ```
 
-##Exercise 6.4
-
-```cpp
-int func()
-{
-    int n, ret = 1;
-    std::cout << "input a number: ";
-    std::cin >> n;
-    while (n > 1) ret *= n--;
-    return ret;
-}
-
-int main()
-{
-    std::cout << func() << std::endl;
-    return 0;
-}
-```
+## [Exercise 6.4](ex6_04.cpp)
 
 ##Exercise 6.5
 

ch06/ex6_04.cpp

@@ -0,0 +1,36 @@
+/*
+=================================================================================
+
+C++ Primer 5th Exercise Answer Source Code
+Copyright (C) 2014-2015 github.com/pezy/CppPrimer
+
+Write a function that interacts with the user, asking for a
+number and generating the factorial of that number. Call this function from
+main.
+
+If you have questions, try to connect with me: pezy<urbancpz@gmail.com>
+
+=================================================================================
+*/
+
+#include <iostream>
+
+void factorial_with_interacts() {
+    int num;
+    std::cout << "Please input a positive number: ";
+    while ( std::cin >> num && num < 0 )
+        std::cout << "Please input a positive number again: ";
+    std::cout << num;
+
+    unsigned long long result = 1;
+    while (num > 1) result *= num--;
+
+    std::cout << "! is ";
+    if ( result ) std::cout << result << std::endl;
+    else std::cout << "too big" << std::endl;
+}
+
+int main()
+{
+    factorial_with_interacts();
+}