Showing numbers in decimal not scientific notation

[Chris Kawa]

@tomy said in Showing numbers in decimal not scientific notation:

I run it in standard mode (ctrl + R).

That's not what I... ugh, nevermind.
So you say you're using QTextStream. Ok, so you have a code similar to this right?

QTextStream foo = ...;
double bar = ...;
foo << bar;

If that's the case then you can do it in a couple of ways:
Switch the stream serialization mode for floating numbers to fixed notation:

QTextStream foo = ...;
foo.setRealNumberNotation(QTextStream::FixedNotation);
double bar = ...;
foo << bar;

or pre-format the number the way you want it and pass the resulting string to the stream:

QTextStream foo = ...;
double bar = ...;
foo << QString::number(bar, 'f');

[tomy]

@Chris-Kawa
What is ...ugh?! I want to learn it! :)

My code is like this:

QString s;
QTextStream (&s) << 12 ;
lineEdit -> setText(s); // It outputs 12 
s.clear();

QTextStream (&s) << "ABC";
lineEdit -> setText(s); // This time it outputs ABC

[Chris Kawa]

12 is not a double, it's an int. 12.0 is a double and 12.0f is a float.
So anyway, like I said earlier, either

QString s;
QTextStream foo(&s);
foo.setRealNumberNotation(QTextStream::FixedNotation);
s << 12.0 ; //assuming you still want that double and not int
lineEdit -> setText(s);

or

QString s;
QTextStream (&s) << QString::number(12.0, 'f');
lineEdit -> setText(s);

but then it's kinda pointless, you can just directly do

lineEdit -> setText(QString::number(12.0, 'f'));

...ugh is the sound you can make when you don't have the energy to explain something, so you just skip it altogether ;)

[VRonin]

no need to use QTextStream in that case:

lineEdit->setText(lineEdit->locale().toString(1257.147862,'f'));

'f' prevents scientific notation, see http://doc.qt.io/qt-5/qstring.html#argument-formats

[tomy]

@VRonin

lineEdit->setText(lineEdit->locale().toString(1257.147862,'f'));

There is no s in your lineEdit!

lineEdit -> setText( // here s should be put!)

[VRonin]

ok, I guess...

QString s;
s=lineEdit->locale().toString(1257.147862,'f');
lineEdit -> setText(s);

[tomy]

@Chris-Kawa said in Showing numbers in decimal not scientific notation:

QString s;
QTextStream (&s) << QString::number(12.0, 'f');
lineEdit -> setText(s);

I used it. It's fine for doubles but when I calculate ints (e.g., 2+3) it shows 5.000000!!
We should make it show the precision only when the result is a double number not an int.

[kshegunov]

@tomy said in Showing numbers in decimal not scientific notation:

I used it. It's fine for doubles but when I calculate ints (e.g., 2+3) it shows 5.000000!!
We should make it show the precision only when the result is a double number not an int.

You either calculate a double or an int, can't be both. Anyway, what you probably want is this:

double calculationResult = 12.0;
QString displayValue = qFuzzyCompare(calculationResult, static_cast<qint64>(calculationResult)) ? QString::number(static_cast<qint64>(calculationResult)) : QString::number(calculationResult, 'f');

[tomy]

@kshegunov

You either calculate a double or an int, can't be both.
Anyway, what you probably want is this:

How can it be acceptable!? All calculator around the world do calculations on both types. Furthermore, when I write 2.3+4.6, it shows: 6.900000!
That is it works fine neither for ints nor for doubles.

double calculationResult = 12.0;
QString displayValue = qFuzzyCompare(calculationResult, static_cast<qint64>(calculationResult) ? QString::number(static_cast<qint64>(calculationResult)) : QString::number(calculationResult, 'f');

Ow my God! Isn't there any simpler way?
Please have a look at Windows built-in calculator. See this how simple and nifty shows results.
Do you say that behind that Windows' calculator there would be such a long statement just for showing numbers in decimal mode, if it were written by C++/Qt?

[kshegunov]

@tomy said in Showing numbers in decimal not scientific notation:

How can it be acceptable!? All calculator around the world do calculations on both types. Furthermore, when I write 2.3+4.6, it shows: 6.900000!

No they do calculation in the widest possible type they support (here it's double) and then display the result as appropriate. Further reading on implicit type promotions in c++ can be found here

Ow my God! Isn't there any simpler way?

This is a simple if-else statement with the notable exception that it compares floating point values as they should be compared.

Do you say that behind that Windows' calculator there would be such a long statement just for showing numbers in decimal mode, if it were written by C++/Qt?

Yes, I'm sure of it. It's probably even much longer as windows is actually written in C.

[tomy]

I used this:

ss = qFuzzyCompare(expression(),
                 static_cast<qint64>(expression()) ?
                 QString::number(static_cast<qint64>(expression())) :
                 QString::number(expression(), 'f'));
 result_box -> setText(ss);

ss is a QString.
expression() returns an int or double value.
result_box is a lineEdit which shows the result of the calculations.

I get this error:
C:\Users\ME\Documents\Qt\My_First_Calculator\my_first_calculator.cpp:81: error: no matching function for call to 'qFuzzyCompare(double, QString)'
QString::number(expression(), 'f'));
^

[kshegunov]

@tomy said in Showing numbers in decimal not scientific notation:

expression() returns an int or double value.

I'm pretty sure that functions returns a string, not an int, nor a double. You need to convert the string to an actual number if you want to use it as such, e.g. see here.

[tomy]

@kshegunov

expression() returns an int or double value.

I'm pretty sure that functions returns a string, not an int, nor a double.

Don't be that sure. :)
I have this method in my code:

double My_First_Calculator::expression()

But I think this error is of that ss is a QString.

[VRonin]

@tomy Did you even try my solution?

[tomy]

@VRonin

Should I use it this way:

QString ss;
ss = result_box -> locale().toString(1257.147862,'f');
QTextStream (&ss) << expression();
result_box -> setText(ss);

?

[VRonin]

@tomy No, don't use QTextStream you don't need something like stringstream to pass numbers to string.

QString ss;
ss = result_box -> locale().toString(expression(),'f');
result_box -> setText(ss);

or more concisely, result_box->setText(result_box->locale().toString(expression(),'f'));

[tomy]

@VRonin said in Showing numbers in decimal not scientific notation:

@tomy No, don't use QTextStream you don't need something like stringstream to pass numbers to string.

QString ss;
ss = result_box -> locale().toString(expression(),'f');
result_box -> setText(ss);

I used it. 2 + 3 = 5.000000 :( :(

[VRonin]

what is result_box and what is inside expression()?

[tomy]

@VRonin

what is result_box

It's a lineEdit.

and what is inside expression()?

It returns only a double value. Consider something simple like:

double My_First_Calculator::expression()
{
   double d1, d2;    // these d1, d2 are gotten from input E.g. d1 = 2, d2 = 3.5
  if(_ch == '+') return d1+d2;  // _ch is a previously defined varible 
 else if (_ch == '-') return d1-d2;  // and so on
}

[tomy]

I simplified the code as follows. This, too, has exactly that problem:

test.h

#ifndef TEST_H
#define TEST_H
#include <QDialog>

class QLineEdit;
class QPushButton;

class test : public QDialog
{
    Q_OBJECT
public:
    test(QWidget* parent = 0);

private slots:
    void expression();

private:
    QLineEdit* result_box;
    QPushButton* equal;
    QPushButton* quit;
};

#endif // TEST_H

test.cpp

#include <QtWidgets>
#include "test.h"

test::test(QWidget* parent) : QDialog(parent)
{
  result_box = new QLineEdit;
  equal = new QPushButton(tr("="));
  quit = new QPushButton(tr("Close"));


  connect(quit, SIGNAL(clicked(bool)), this, SLOT(close()));
  connect(equal,SIGNAL(clicked(bool)), this, SLOT(expression()));

  QHBoxLayout* layout = new QHBoxLayout;
  layout -> addWidget(result_box);
  layout -> addWidget(equal);
  layout -> addWidget(quit);

  setLayout(layout);
}

//******************

void test::expression()
{
    QString ss;
    double d = 1000000;
    QTextStream (&ss) << d;
    result_box -> setText(ss);
}

And main.cpp

#include <QApplication>
#include "test.h"

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    test t;
    t.show();

   return app.exec();
}

Just run it and click on the = button.