Oleg Popkov authored Jun 07, 2020 and Maximilian Schiller committed Jun 07, 2020

In brief, KCalc uses a stack in `CalcEngine` for both numbers and operations in order to ensure the correct operation evaluation order (such that `2 + 2 * 2 = 6`) and support parentheses. Operations are pushed along with currently displayed numerical values. KCalc also checks whether it should push the operation onto the stack or just replace a pushed one with the new one without changing the associated number (so that `5 + - 3 = 2`), and for this it uses a flag changed by calling the `CalcEngine::setOnlyUpdateOperation` method. Obviously, this flag must be cleared after a number is entered by any method, but it only happens if a number is entered manually. As a result, inserting a number as a whole, whether as a constant or by pasting from the clipboard, results in replacing the preceding operation with the succeeding one without storing the number in question, unless the succeeding operation is `=` or `%`.

BUG: 412401