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Showing numbers in decimal not scientific notation

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  • tomyT tomy

    @Chris-Kawa
    I run it in standard mode (ctrl + R).

    Chris KawaC Offline
    Chris KawaC Offline
    Chris Kawa
    Lifetime Qt Champion
    wrote on last edited by
    #8

    @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');
    
    tomyT 1 Reply Last reply
    3
    • Chris KawaC 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');
      
      tomyT Offline
      tomyT Offline
      tomy
      wrote on last edited by tomy
      #9

      @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
      
      1 Reply Last reply
      0
      • Chris KawaC Offline
        Chris KawaC Offline
        Chris Kawa
        Lifetime Qt Champion
        wrote on last edited by
        #10

        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 ;)

        tomyT 1 Reply Last reply
        2
        • VRoninV Offline
          VRoninV Offline
          VRonin
          wrote on last edited by VRonin
          #11

          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

          "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
          ~Napoleon Bonaparte

          On a crusade to banish setIndexWidget() from the holy land of Qt

          tomyT 1 Reply Last reply
          0
          • VRoninV 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

            tomyT Offline
            tomyT Offline
            tomy
            wrote on last edited by
            #12

            @VRonin

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

            There is no s in your lineEdit!

            lineEdit -> setText( // here s should be put!)
            
            1 Reply Last reply
            0
            • VRoninV Offline
              VRoninV Offline
              VRonin
              wrote on last edited by
              #13

              ok, I guess...

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

              "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
              ~Napoleon Bonaparte

              On a crusade to banish setIndexWidget() from the holy land of Qt

              1 Reply Last reply
              1
              • Chris KawaC 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 ;)

                tomyT Offline
                tomyT Offline
                tomy
                wrote on last edited by tomy
                #14

                @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.

                kshegunovK 1 Reply Last reply
                0
                • tomyT 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.

                  kshegunovK Offline
                  kshegunovK Offline
                  kshegunov
                  Moderators
                  wrote on last edited by kshegunov
                  #15

                  @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');
                  

                  Read and abide by the Qt Code of Conduct

                  tomyT 1 Reply Last reply
                  1
                  • kshegunovK 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');
                    
                    tomyT Offline
                    tomyT Offline
                    tomy
                    wrote on last edited by tomy
                    #16

                    @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?

                    kshegunovK VRoninV 2 Replies Last reply
                    0
                    • tomyT 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?

                      kshegunovK Offline
                      kshegunovK Offline
                      kshegunov
                      Moderators
                      wrote on last edited by kshegunov
                      #17

                      @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.

                      Read and abide by the Qt Code of Conduct

                      1 Reply Last reply
                      1
                      • tomyT Offline
                        tomyT Offline
                        tomy
                        wrote on last edited by tomy
                        #18

                        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'));
                        ^

                        kshegunovK 1 Reply Last reply
                        0
                        • tomyT 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'));
                          ^

                          kshegunovK Offline
                          kshegunovK Offline
                          kshegunov
                          Moderators
                          wrote on last edited by
                          #19

                          @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.

                          Read and abide by the Qt Code of Conduct

                          tomyT 1 Reply Last reply
                          0
                          • kshegunovK 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.

                            tomyT Offline
                            tomyT Offline
                            tomy
                            wrote on last edited by tomy
                            #20

                            @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.

                            kshegunovK 1 Reply Last reply
                            0
                            • tomyT 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?

                              VRoninV Offline
                              VRoninV Offline
                              VRonin
                              wrote on last edited by
                              #21

                              @tomy Did you even try my solution?

                              "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                              ~Napoleon Bonaparte

                              On a crusade to banish setIndexWidget() from the holy land of Qt

                              tomyT 1 Reply Last reply
                              0
                              • VRoninV VRonin

                                @tomy Did you even try my solution?

                                tomyT Offline
                                tomyT Offline
                                tomy
                                wrote on last edited by
                                #22

                                @VRonin

                                Should I use it this way:

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

                                ?

                                VRoninV 1 Reply Last reply
                                0
                                • tomyT 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);
                                  

                                  ?

                                  VRoninV Offline
                                  VRoninV Offline
                                  VRonin
                                  wrote on last edited by
                                  #23

                                  @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'));

                                  "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                  ~Napoleon Bonaparte

                                  On a crusade to banish setIndexWidget() from the holy land of Qt

                                  tomyT 1 Reply Last reply
                                  0
                                  • VRoninV 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'));

                                    tomyT Offline
                                    tomyT Offline
                                    tomy
                                    wrote on last edited by
                                    #24

                                    @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 :( :(

                                    1 Reply Last reply
                                    0
                                    • VRoninV Offline
                                      VRoninV Offline
                                      VRonin
                                      wrote on last edited by
                                      #25

                                      what is result_box and what is inside expression()?

                                      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                                      ~Napoleon Bonaparte

                                      On a crusade to banish setIndexWidget() from the holy land of Qt

                                      tomyT 1 Reply Last reply
                                      0
                                      • VRoninV VRonin

                                        what is result_box and what is inside expression()?

                                        tomyT Offline
                                        tomyT Offline
                                        tomy
                                        wrote on last edited by tomy
                                        #26

                                        @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
                                        }
                                        
                                        1 Reply Last reply
                                        0
                                        • tomyT Offline
                                          tomyT Offline
                                          tomy
                                          wrote on last edited by tomy
                                          #27

                                          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.

                                          tomyT 1 Reply Last reply
                                          0

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