In system programming, you can use the `if` and `if..else` statements/evolution to run a block of code when a specific condition is met.
For example, we suggest a student can be assigned grades to a subject based on their in total score.
* if the score is upon 80, then assign grade A
* if the score is upon 70, then assign grade B
* if the score is upon 60, then assign grade C
## Boolean Expression In Rust
At First we study about `if..else` evolutions, let’s speedily understand boo