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Showing numbers in decimal not scientific notation

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  • tomyT tomy

    Hi all,

    In may app I have a double variable:

    double d;
    

    When the result of 10^6 goes to that variable, it shows it this way: 1e+06
    How to do to make the app show the result in decimal, 1000000?

    K Offline
    K Offline
    koahnig
    wrote on last edited by
    #2

    @tomy
    Where do you want to see a fixed number?

    Vote the answer(s) that helped you to solve your issue(s)

    tomyT 1 Reply Last reply
    0
    • Chris KawaC Offline
      Chris KawaC Offline
      Chris Kawa
      Lifetime Qt Champion
      wrote on last edited by
      #3

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

      it shows it this way

      What is "it"? Where do you view the variable? In the debugger? On the standard output? In a text widget? What (if any) function do you use to output the variable?

      tomyT 1 Reply Last reply
      0
      • M Offline
        M Offline
        mostefa
        wrote on last edited by mostefa
        #4

        Hi @tomy

        I don't know if this is what you want, but if you wanna keep only the decimal part of your double you can cast your double to int, you can do something like this :

        (int)(10^6)

        tomyT 1 Reply Last reply
        0
        • K koahnig

          @tomy
          Where do you want to see a fixed number?

          tomyT Offline
          tomyT Offline
          tomy
          wrote on last edited by
          #5

          @koahnig
          The number, "1e+06", will be sent to a QTextStream which has the address of a QString. Then that string will be sent to a lineEdit. and finally LineEdit will show the number in scientific notation.

          1 Reply Last reply
          0
          • Chris KawaC Chris Kawa

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

            it shows it this way

            What is "it"? Where do you view the variable? In the debugger? On the standard output? In a text widget? What (if any) function do you use to output the variable?

            tomyT Offline
            tomyT Offline
            tomy
            wrote on last edited by
            #6

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

            Chris KawaC 1 Reply Last reply
            0
            • M mostefa

              Hi @tomy

              I don't know if this is what you want, but if you wanna keep only the decimal part of your double you can cast your double to int, you can do something like this :

              (int)(10^6)

              tomyT Offline
              tomyT Offline
              tomy
              wrote on last edited by
              #7

              @mostefa
              No dear. I don't want it.

              1 Reply Last reply
              0
              • 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
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