This was run on a computer and the result was 3.

This problem mainly depends on self-increase and self-decrease, and the former is behind.

++i means that I will participate in other operations after adding 1; And i++ means that the value of I increases 1 after I participate in the operation.

So it can be seen as

1 +0 +2 = 3

However, it is not recommended that manipulated numbers appear in the same sentence many times, which will not only make the meaning of the program difficult to understand, but also greatly reduce the readability, and may also lead to different results of different compilers or compiler versions.