@sirivias is correct, you can’t use 45voltage as a variable name.
C++ error texts are often confusing, you probably saw something like…
…which might make no sense at all to a carbon-based lifeform’s brain late at night.
What you can do is google that message unqualified-id and you’ll probably find something that punts you in the right direction.
I often find StackOverflow to be helpful and reliable.
In this case, the compiler is complaining about the variable name 45voltage.
A variable name has to start with an alphabetic character, upper or lower-case, or the underscore character “_”. Then the rest of the name can be any combination of alphanumeric characters & underscores (but not only underscores).
So valid variable names here might be: voltage45, voltage_45, _45voltage, Voltage45, v45, V45, or even _45.
As you get into C++ you’ll work out your own plan for meaningful variable names, and discover other tools like arrays and switches that might express your original code much more simply and clearly (and debugably, if that can be a word) in just a few lines.
Enjoy the journey.