Incrementing a number in qt c++

[Lasith]

In my code I need to increment an integer used by 2 methods(button clicks)! 1 method is used to display the integer(starting value is 1) in a line edit when a button is clicked! The other button is used to increment the number! I need to declare the integer in the header file to be used by the two methods! But in the header file we can declare only static constant so when I increment the error I get an error! How can I avoid this?

void MainWindow::on_pushButton_2_clicked()
{
ui->lineedit->text(QString::number(i));
}
void MainWindow::on_pushButton_2_clicked(){
i++;
}

[jsulm]

@Lasith Just declare it as member variable in MainWindow class:

class MainWindow
{
    ...
private:
    int i;
}

Note: there is no such thing as "qt c++".

[Lasith]

@jsulm Thanx but I get the error message "only static const integral data members can be initialized within a class” :(

[jsulm]

@Lasith I guess you did it like this?

class MainWindow
{
    ...
private:
    int i = 0;
}

This is supported in C++11 and newer.
Do it like this:

class MainWindow
{
    ...
private:
    int i;
}

// in mainwindow.cpp
MainWindow::MainWindow(): i(0)
{
}

This are C++ basics, you should really take some time to learn C++.
As alternative you can enable C++11 support (will only work if your compiler supports it!). To do so add this to your pro file:

CONFIG += c++11

Run qmake and rebuild.

[Lasith]

@jsulm Thanx but where is

MainWindow::MainWindow():
{
}

to put i(0) ?

I only find

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)

in my mainwindow.cpp

[jsulm]

@Lasith Just extend the existing constructor:

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow),
i(0)
{
...
}

[SGaist]

Hi,

To add to @jsulm which version of Qt are you using ? Since 5.7, C++11 is mandatory.

[Lasith]

@SGaist 5.2

[Lasith]

@jsulm Thanx for your great help! I am new to Qt and c++ programming

[SGaist]

Then please consider upgrading to a more recent version, we are currently at Qt 5.9.

[Lasith]

This post is deleted!

[mrjj]

@Lasith
thats just
i=0;
in any function that is member of the class.