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Showing numbers in decimal not scientific notation

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  • 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
                                        • tomyT 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.

                                          tomyT Offline
                                          tomyT Offline
                                          tomy
                                          wrote on last edited by tomy
                                          #28

                                          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));
                                          
                                          K 1 Reply Last reply
                                          0

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