1.单行注释一般放在语句的上方：
// cout and endl live in the iostream library
std::cout << "Hello world!" << std::endl;
2.多行注释写法：
/* This is a multi-line comment.
* the matching asterisks to the left
* can make this easier to read
*/
3.注释的用处
.At the library, program, or function level, describe what
.Inside the library, program, or function, describe how
.At the statement level, describe why
通俗点就是：
（1）描述该块代码是什么；
（2）描述该块代码如何实现；
（3）描述该块代码为什么要如此实现；
接下来举些例子：
(1)what
// This program calculate the student's final grade based on his test and homework scores.
(2)how
/* To calculate the final grade, we sum all the weighted midterm and homework scores
and then divide by the number of scores to assign a percentage. This percentage is
used to calculate a letter grade.
*/
// To generate a random item, we're going to do the following:
// 1) Put all of the items of the desired rarity on a list
// 2) Calculate a probability for each item based on level and weight factor
// 3) Choose a random number
// 4) Figure out which item that
(3)why
// We need to divide items by 2 here because they are bought in pairs
cost = items / * storePrice;