Showing numbers in decimal not scientific notation

[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?

[koahnig]

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

[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?

[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)

[tomy]

@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.

[tomy]

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

[tomy]

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

[Chris Kawa]

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

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

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

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

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

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

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

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

[tomy]

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

My code is like this:

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

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

[Chris Kawa]

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

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

or

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

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

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

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

[VRonin]

no need to use QTextStream in that case:

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

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

[tomy]

@VRonin

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

There is no s in your lineEdit!

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

[VRonin]

ok, I guess...

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

[tomy]

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

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

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

[kshegunov]

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

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

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

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

[tomy]

@kshegunov

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

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

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

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

[kshegunov]

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

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

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

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

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

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

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

[tomy]

I used this:

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

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

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

[kshegunov]

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

expression() returns an int or double value.

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

[tomy]

@kshegunov

expression() returns an int or double value.

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

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

double My_First_Calculator::expression()

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