My first attempt to create a calculator as a novice in Qt programming

tomy

@mrjj said in My first attempt to create a calculator as a novice in Qt programming:

Hi
All is debatable but my points would be :
You are using good variable names but Im not crazy with underscores.
Seen code where used a lot and it very hard to read.

Hi. :)

You are right. It's hard for reading. I will put enough white spaces and comments when it is finished. :)
And what do you mean by "not crazy with underscore" please? (not a native speaker. :( )

Not issue here but now its mentioned.
Also , choose a style for variable naming and use it all over.
QLineEdit* lineEdit; <<< qt style
QSignalMapper* signalMapper; << qt style
QString temp_text; << other style

How to choose a style please?

Also
void My_First_Calculator::reset()
why send a "c" to show_number to reset?
Why not directly

void My_First_Calculator::reset()
{
temp_text.clear();
lineEdit -> setText("");
}

Yeah, very handy, thanks. I applied it. :)

2- Apparently since I didn't use the Designer
Well if you do not use UI files, then you just adjust from code.
with resize or setGeometry.
However, for app like yours, one would use layout to make it auto scale the buttons to any size if dialog is resized.
http://doc.qt.io/qt-5/layout.html

Apparently, in my form until here, using only HBoxLayout, VBoxLayout, and GridLayout are fine. Do you not agree?

mrjj

Hi :)

And what do you mean by "not crazy with underscore" please? (not a native speaker. :( )

Means, I don't like so much. ( reading it )

How to choose a style please?

Well, Thats is mostly what you like. Sometimes in teams , we must agree but if you are
working solo then just choose one and stick to it.
Its mostly about if you write it like
SomeName
someName
somename
some_name

so the important part is just to name it the same way each time and not mixing it.

Apparently, in my form until here, using only HBoxLayout, VBoxLayout, and GridLayout are fine. Do you not agree?
Those are fine and should make it scale all when you resize the window.

tomy

@mrjj said in My first attempt to create a calculator as a novice in Qt programming:

Hi :)

And what do you mean by "not crazy with underscore" please? (not a native speaker. :( )

Means, I don't like so much. ( reading it )

How to choose a style please?

Well, Thats is mostly what you like. Sometimes in teams , we must agree but if you are
working solo then just choose one and stick to it.
Its mostly about if you write it like
SomeName
someName
somename
some_name

so the important part is just to name it the same way each time and not mixing it.

Apparently, in my form until here, using only HBoxLayout, VBoxLayout, and GridLayout are fine. Do you not agree?
Those are fine and should make it scale all when you resize the window.

Thank you :)

I put some other widgets as well, like another lineEdit for the results and so on.
Now I come across two other questions. :)

1- Assume I have a button like this:

QPushButton* two = new QPushButton(tr("2"))

How do I send that string ("2") to the show_number(const QString& text) so that it will be shown by the lineEdit in the form when running the program? I mean without using a signalMapper? Apparently I can't use parameters in connect to send for that function. :(

2- Consider I want to store the contents the lineEdit into a vector of char (so that I will be able to calculate the contents later). How to do it lease?

EDITED!

jsulm

@tomy

In the slot:

QString s = reinterpret_cast<QPushButton*>(sender())->text();

Why? If user enters number 123, why do you want to store this number in a vector like ['1', '2', '3']? It is actually a vector of strings. For that you can split the string, see http://doc.qt.io/qt-5/qstring.html#split

tomy

@jsulm said in My first attempt to create a calculator as a novice in Qt programming:

@tomy

In the slot:
QString s = reinterpret_cast<QPushButton*>(sender())->text();
Why? If user enters number 123, why do you want to store this number in a vector like ['1', '2', '3']? It is actually a vector of strings. For that you can split the string, see http://doc.qt.io/qt-5/qstring.html#split

Because the user types something like "123+256" so it con't be seemingly stored as a (vector of) int.

Guys, I think the program is much more complicated than these items. The app should be able to separate the operands from operators. And also it should be able to observe the priority of the operators, for example:
2+3*4 to be 14 not 20.

What methods would you generally use for each step?

I'm thinking of two tools: first the Dijkstra's algorithm to make the statement a Reverse Polish Notation and then use a stack for calculating. Do you agree?

jsulm

@tomy said in My first attempt to create a calculator as a novice in Qt programming:

Because the user types something like "123+256" so it con't be seemingly stored as a (vector of) int.

But it can be stored as a vector of strings: ["123", "+", "256"] - that's what I said.
Vector of char would be: ['1', '2', '3', '+', '2', '5, '6']

tomy

@jsulm said in My first attempt to create a calculator as a novice in Qt programming:

@tomy said in My first attempt to create a calculator as a novice in Qt programming:

Because the user types something like "123+256" so it con't be seemingly stored as a (vector of) int.

But it can be stored as a vector of strings: ["123", "+", "256"] - that's what I said.
Vector of char would be: ['1', '2', '3', '+', '2', '5, '6']

Buttons send each number as a string; "1", "3", "+" and so on. When the user types "123+256" a string containing "123+256" will be shown on lineEdit. Hence, I should somehow parse to make operators and operands detached. That was why (at the time) I thought of a vector of chars.
But anyway, I'm thinking of a good algorithm to cover expressions like this, that is when we input all of this line once, it makes a correct result:
2+30-12/3+(4^8-1)+sqrt(65)*2.12

tomy

Hi all,

It's done. :) :) :)
The app is finished and it works fine. Please download it from here:
http://www.4shared.com/file/H5brsoaPce/My_First_Calculator.html

It needs only a few .dll files for to be run.

I have some question please:
1- How to change the title of the window from "My_First_Calculator" to "A Qt Calculator!"?
2- I want to design the buttons better from the size, position end etc. How can I do this?
3- Is it possible to make it appear like a professional app?

kshegunov

@tomy said in My first attempt to create a calculator as a novice in Qt programming:

But anyway, I'm thinking of a good algorithm to cover expressions like this, that is when we input all of this line once, it makes a correct result:

Reverse polish notation is what you're probably searching for. See here.

VRonin

This is a infix to postfix conversion for the 4 basic operations and parenthesis I wrote some time ago. it works just for integers but it's a start. once you have the string in postfix (i.e. reverse polish) the calculation is very easy

Edit

Ignore my sh*ty code, see http://rosettacode.org/wiki/Parsing/Shunting-yard_algorithm#C for an idea of converting infix to postfix. thanks @kshegunov for talking some sense into me

tomy

Thank you guys but the work is done!
I appreciate your reactions so much.
Please help me on these questions:

@tomy said in My first attempt to create a calculator as a novice in Qt programming:

Hi all,

It's done. :) :) :)
The app is finished and it works fine. Please download it from here:
http://www.4shared.com/file/H5brsoaPce/My_First_Calculator.html

It needs only a few .dll files for to be run.

I have some question please:
1- How to change the title of the window from "My_First_Calculator" to "A Qt Calculator!"?
2- I want to design the buttons better from the size, position end etc. How can I do this?
3- Is it possible to make it appear like a professional app?

kshegunov

@tomy said in My first attempt to create a calculator as a novice in Qt programming:

How to change the title of the window from "My_First_Calculator" to "A Qt Calculator!"?

You can use QWidget::setText on the main window. That should work.

I want to design the buttons better from the size, position end etc. How can I do this?

I haven't downloaded the code as I haven't the time to check it out just now, but putting the widgets in layouts should arrange them well.

Is it possible to make it appear like a professional app?

Well, you could polish the look a bit with a stylesheet, look up the docs on them.

tomy

@kshegunov
Thank you. Please download the app and look how it appears. Until that time I will read the link on docs. Thanks.