diff --git a/NumericStrings/NumericString.cpp b/NumericStrings/NumericString.cpp
index 6c60d35..37b4909 100644
--- a/NumericStrings/NumericString.cpp
+++ b/NumericStrings/NumericString.cpp
@@ -1,84 +1,74 @@
-/* 
- * Question Description:
- * (Question 12 in <Coding Intervies>) How do you check whether a string stands for a number or not? 
- * Numbers include positive and negative integers and floats. For example, strings “+100.”, “5e2”, “-.123”, “3.1416”, and “-1E-16” 
- * stand for numbers, but “12e”, “1a3.14”, “1.2.3”, “+-5”, and “12e+5.4” do not. 
+/*
+* Question Description:
+* (Question 12 in <Coding Intervies>) How do you check whether a string stands for a number or not?
+* Numbers include positive and negative integers and floats. For example, strings "+100.", "5e2", "-.123", "3.1416", and "-1E-16"
+* stand for numbers, but "12e", "1a3.14", "1.2.3", "+-5", and "12e+5.4" do not.
 */
 
 #include <stdio.h>
 
-void scanDigits(char** string);
-bool isExponential(char** string);
+bool scanUnsignedInteger(const char** str);
+bool scanInteger(const char** str);
 
-bool isNumeric(char* string)
+// the form of exponent is like A[.[B]][e|EC] or .B[e|EC]
+// where A and C is an integer with or without sign, and B is an unsigned integer
+bool isNumeric(const char* str)
 {
-    if(string == NULL)
+    if (str == NULL)
         return false;
 
-    if(*string == '+' || *string == '-')
-        ++string;
-    if(*string == '\0')
-        return false;
+    bool numeric = scanInteger(&str);
 
-    bool numeric = true;
-
-    scanDigits(&string);
-    if(*string != '\0')
-    {
-        // for floats
-        if(*string == '.')
-        {
-            ++string;
-            scanDigits(&string);
-            
-            if(*string == 'e' || *string == 'E')
-                numeric = isExponential(&string);
-        }
-        // for integers
-        else if(*string == 'e' || *string == 'E')
-            numeric = isExponential(&string);
-        else
-            numeric = false;
+    // for floats
+    // you can have no integer part such as .123 means 0.123
+    // in the meanwhile, you can have no decimal part such as 233. means 233.0
+    // what's more, 233.666 is OK also.
+    if (*str == '.') {
+        ++str;
+        numeric = scanUnsignedInteger(&str) || numeric;
     }
 
-    return numeric && *string == '\0';
-}
+    // for exponent
+    if (*str == 'e' || *str == 'E') {
+        ++str;
+        numeric = scanInteger(&str) && numeric;
+    }
 
-void scanDigits(char** string)
-{
-    while(**string != '\0' && **string >= '0' && **string <= '9')
-        ++(*string);
+    return numeric && *str == '\0';
 }
 
-bool isExponential(char** string)
+bool scanUnsignedInteger(const char** str)
 {
-    if(**string != 'e' && **string != 'E')
-        return false;
-        
-    ++(*string);
-    if(**string == '+' || **string == '-')
-        ++(*string);
+    const char* pBefore = *str;
+    while (**str != '\0' && **str >= '0' && **str <= '9')
+        ++(*str);
 
-    if(**string == '\0')
-        return false;
+    // return true when there are some digits in str
+    return *str > pBefore;
+}
 
-    scanDigits(string);
-    return (**string == '\0') ? true : false;
+// an integer's form is like [+|-]B, where B is an unsigned integer
+bool scanInteger(const char** str)
+{
+    if (**str == '+' || **str == '-')
+        ++(*str);
+    return scanUnsignedInteger(str);
 }
 
 // ==================== Test Code ====================
 
-void Test(char* testName, char* string, bool expected)
+void Test(const char* testName, const char* str, bool expected)
 {
-    if(testName != NULL)
+    if (testName != NULL)
         printf("%s begins: ", testName);
 
-    if(isNumeric(string) == expected)
+    if (isNumeric(str) == expected)
         printf("Passed.\n");
     else
         printf("FAILED.\n");
 }
 
+
 int main(int argc, char* argv[])
 {
     Test("Test1", "100", true);
@@ -99,6 +89,9 @@ int main(int argc, char* argv[])
     Test("Test13", "1.2.3", false);
     Test("Test14", "+-5", false);
     Test("Test15", "12e+5.4", false);
+    Test("Test16", ".", false);
+    Test("Test17", ".e1", false);
+    Test("Test18", "+.", false);
 
-	return 0;
+    return 0;
 }