Showing numbers in decimal not scientific notation

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.

tomy

I think I should write a code for it like this:

if( d is like an int number)
    result_box -> setText(QString::number(d , 'f', 0));
else if ( d is a double number with n numbers after point)
   result_box -> setText(QString::number(d , 'f', n));

koahnig

@tomy
Maybe you should have a look to the docs as well. E.g. here

In case of integer assignment that would be:

int i = 10;
result_box -> setText ( QString::number( i ) );

kshegunov

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

Don't be that sure. :)

Yes! There's a typo in the code ... :)

ss = qFuzzyCompare(expression(),
                 static_cast<qint64>(expression()) ? //< Missing a )
                 QString::number(static_cast<qint64>(expression())) :
                 QString::number(expression(), 'f')); //< Extra )

What you want is to have the if with qFuzzyCompare, not with the static cast. It should rather read like this:

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

If you wish you can of course use the usual if-else construct, not the ternary operator, so the last snippet'd be equivalent to:

if (qFuzzyCompare(expression(), static_cast<qint64>(expression()))
    ss = QString::number(static_cast<qint64>(expression()));
else
    ss = QString::number(expression(), 'f');

tomy

This post is deleted!

tomy

@kshegunov

What you want is to have the if with qFuzzyCompare, not with the static cast. It should rather read like this:
ss = qFuzzyCompare(expression(), static_cast<qint64>(expression())) ?
                 QString::number(static_cast<qint64>(expression())) :
                 QString::number(expression(), 'f');
If you wish you can of course use the usual if-else construct, not the ternary operator, so the last snippet'd be equivalent to:
if (qFuzzyCompare(expression(), static_cast<qint64>(expression()))
    ss = QString::number(static_cast<qint64>(expression()));
else
    ss = QString::number(expression(), 'f');

Sorry, I don't know how I tested it but it doesn't work as it's expected! :(
for example:
2 + 3 = 5 OK
10 ^ 6 = 1000000 OK
2 + 1.5 = 3.500000 !!!

That is, the function QString::number(expression(), 'f'); (with the default precision 6) shows all range of precision whether it's need or not!

Maybe it's what we need:
http://doc.qt.io/qt-5/qtextstream.html#setRealNumberNotation
But how to use it? Docs doesn't offer a little example of it to show how beginners should use it. !!!!!!
(Docs are not for learners/beginners, they are for professionals — if they are professional, so they don't need Docs much => Docs are not useful)