When the sum of a + b is too large, an overflow occurs. The long long here is signed long long. After overflow, it is truncated according to the number of digits of the long long, and then converted into a decimal number, which may become a negative number. Situation, then something went wrong.
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
When the sum of a + b is too large, an overflow occurs. The long long here is signed long long. After overflow, it is truncated according to the number of digits of the long long, and then converted into a decimal number, which may become a negative number. Situation, then something went wrong.