diff --git a/practical_exercises/10_day_practice/day7/一元运算符/秒钟自增运算.cpp b/practical_exercises/10_day_practice/day7/一元运算符/秒钟自增运算.cpp
index 1a63193..f420d36 100644
--- a/practical_exercises/10_day_practice/day7/一元运算符/秒钟自增运算.cpp
+++ b/practical_exercises/10_day_practice/day7/一元运算符/秒钟自增运算.cpp
@@ -1,4 +1,4 @@
-//���һ��ʱ����Time�����ܹ�������ӵ��������㡣
+//设计一个时间类Time，它能够完成秒钟的自增运算。
 
 #include<iostream>
 using namespace std;
@@ -9,7 +9,7 @@ class Time{
     public:
         Time(int h,int m, int s);
         Time operator++();
-        //��Ԫ������Ҫ����
+        //友元重载需要参数
         friend Time operator--(Time &t);
         void display(); 
 };
@@ -42,14 +42,14 @@ Time Time::operator++(){
 }
 Time operator--(Time &t){
     --t.second;
-    if (t.second>=60){
-        t.second=0;
-        ++t.minute;
-        if(t.minute>=60){
-            t.minute=0;
-            ++t.hour;
-            if(t.hour>=24)
-                t.hour=0;
+    if (t.second<0){
+        t.second=59;
+        --t.minute;
+        if(t.minute<0){
+            t.minute=59;
+            --t.hour;
+            if(t.hour<0)
+                t.hour=23;
         }
     }
     return t;  
@@ -61,9 +61,9 @@ int main(int argc, char const *argv[])
 {
     Time t1(23,59,59);
     t1.display();
-    ++t1; //��ʽ����
+    ++t1; //隐式调用
     t1.display();
-    t1.operator++(); //��ʽ����
+    t1.operator++(); //显式调用
     t1.display();
     Time t2(24,60,60);
     t2.display();