Qt - creating a complex "calculator"

Question

I am building an application that requires a graphical interface for a calculation process. The calculation is basically a formula written by the user to be evaluated with QScriptEngine - ie, Javascript.

The thing is I'm having trouble breaking down the problem into smaller steps. The general objectives are as follows:

• The values that are to be used in a formula report to properties of items. The items are already created and have a list of properties with which I populate a QTableWidget.
• By dragging/droping from the table to a QTextEdit, I'm creating a string with some rich-formating to help the users read the formula more intuitively. Basically, each item on the table has a certain color, so in the QTextEdit, when an item is dropped, it gets a background-color formatting with the same color, and displays the property's name; something like: <span style='background-color:red;'> propertyName </span>

The drag/drop interface as well as the formating is coded and working as expected. But now I have a few problems:

• some items have properties with the same name. If I create the formula with two different properties (from different items) that have the same name, I can't track the property's value backwards without ambiguity - I was thinking of string compare/string replace the property's name with its value and then calculate with evaluate().

I have been breaking my head on how to get around this and I thought of creating a QMultiMap to hold the item: [property, value] relationships, and then, replacing on the string that will be evaluated. But again, I would need to check form which item the property came from, and I don't know how I can do that.

I'm new to Qt/C++ and I know that most of my code has some big faulty practices, and its being done more in the way of hacking my way through the objectives I require, more than building a good structure - so every new problem gets a more complex solution each time.

Even so, how would you suggest I should tackle this problem? By this time I think it is better to not post my code just yet, because it is too long (and probably painful) to look at. If someone requires a specific portion to better understand the context of the problem, let me know and I'll post here.

Also, I have had other question here in SO when I started to think about this - might be useful to check for context: here.

UPDATE:

In reply to @Riateche's comment:

Imagine this scenario:

Item A : [property1, value1]
         [property2, value2]

Item B : [property1, value3]
         [property2, value4]

Now, imagine the user wants to perform ItemA.property1 * ItemB.property1:

• I want him to see property1 * property1 - but notice that the background-color of each should be different;
• I could place in the QTextEdit something like: <span style='background-color:red;'> property1 </span> * <span style='background-color:blue;'> property1 </span>
• what I actually want to evaluate (to calculate) is: value1 * value3 - in which these represent double types.

UPDATE 2

After thinking a little bit about this, while @Riateche's approach seems simple, I wasn't able to find a way change a tag's attribute (at least in rich text, maybe there is one with QWebkit, but that is not what I need). So I was thinking if building another string (that will be evaluated), at the same time the user builds a string with drag and drop. For instance, let's imagine the user drags and drops something like:

property1 * property1

At the same time I would build other string that contained

value1 * value3

And this would be the evaluated string. Even so, the problem with the user editing the string would still be there - if the user changes the drag/drop string, I need to update the evaluation string again -requiring me to once again check the origin of the data. Any other ideas?

Answer 1

You should put all information important for the formula evaluation to the text edit. You can make it invisible to user. For example, you can put the following to the text edit:

<span style='background-color:red;'><a name='Item A,property1'></a>property1</span>

The Item A,property1 text will be invisible to user, but textEdit->toHtml() result will contain it.