How to select a variable and enter it?

Question

Command line

The option with displaying the equation and entering data in turn is clear how to do it and then updating the screen.
But how to do it in menu view? Those. there is: a cursor that can be moved - select a parameter - enter data - select the next parameter - enter - when all values ​​​​are entered, a calculation will occur or by clicking in the "total" menu, a calculation will occur.

An example of what it should look like

a + b + c = 0
> a: 2
b:
c:

a + b + c = 0
a: 2
> b: 12
c:

a + b + c = 0
a: 2
b: 12
> c: 5

a + b + c = 19
a: 2
b: 12
> c: 5

либо

a + b + c = 19
a: 2
b: 12
c: 5
> итог

Answer 1

The class Consolehas all the necessary methods, and wait for a keystroke, and set the cursor to the desired position, and even read the current cursor coordinates if you suddenly forgot to save them.
Those. when you click down, you need to:
- check that there is an item below at all
- update the current line to remove >
it - update the item below where to display >
- wait for the key to be pressed