[SOLVED] "Round" double

beowulf

Hello guys, i'm with a problem. (I think it's simple)

I'm with a double number: 52.48, and i want to round it to 52.4 only. Without the last number, that in this case is "8".

leon.anavi

I believe that the "static method number of class QString":http://qt-project.org/doc/qt-5.0/qtcore/qstring.html#number-2 may help you:

@QString::number( 52.48, 'f', 1);@

beowulf

It's returning "52.5", i want to return "52.4".

Understand?

Thanks.

leon.anavi

[quote author="l3e0wulf" date="1362577800"]It's returning "52.5", i want to return "52.4".

Understand?

Thanks.[/quote]

I don't know a built-in method that will return you this results but you can easily write your own method. Covert the double to string and remove the unnecessary digits from its end.

Code_ReaQtor

[quote author="l3e0wulf" date="1362577800"]It's returning "52.5", i want to return "52.4".

Understand?

Thanks.[/quote]

What I can say is that the principle of "Rounding" won't apply here.

Maybe you can convert your number to QString using QString::number() then use QRegExp rx("(\d+.\d)") or something similar.

beowulf

Look my problem.

I have two double.

One: 52.48
Two: 52.4

I want to know when the "Two - 52.4" number is like the "One - 52.48", and I realised the "One" is always one number different! The last number.

When I put QString::number("52.48", 'f', 1); it's return 52.5 and in "52.4". It's return: "52.4".

Code_ReaQtor

[quote author="l3e0wulf" date="1362579716"]
When I put QString::number("52.48", 'f', 1); it's return 52.5 and in "52.4". It's return: "52.4".[/quote]

Because you need to put "2" in the third parameter. Then remove the last number at the end.
@ QString::number("52.48", 'f', 2);@

The third parameter is the "precision", using 3 or more will automatically append 0's, AFAIK.
@ QString::number("52.48", 'f', 4); //it will result to "52.4800"@

BelenMuñoz

I think one of the problems is that 52.48 is never like 52.4, if you round it, it's (always) 52.5, so I don't think you'll find a way to solve your problem using numeric types.
I agree with Leon and Core_ReaQtor you can use QString to transform your number, first passing double to QString, transforming it and then passing it to double again.
It's a little "cutre" as we say in Spain (I think it's stingy in english), but I don't have a better idea.

Regards!!

beowulf

When i put QString::number("52.4", 'f', 2); i'ts return: "52.40"
When i put QString::number("52.48", 'f', 2); i'ts return: "52.48"

When i put QString::number("52.4", 'f', 1); i'ts return: "52.4"
When i put QString::number("52.48", 'f', 1); i'ts return: "52.5"

When i put QString::number("52.4", 'f', 2); i'ts return: "52.40"
When i put QString::number("52.48", 'f', 1); i'ts return: "52.5"

When i put QString::number("52.4", 'f', 1); i'ts return: "52.4"
When i put QString::number("52.48", 'f', 2); i'ts return: "52.48"

beowulf

BelenMuñoz:

bq. I agree with Leon and Core_ReaQtor you can use QString to transform your number, first passing double to QString, transforming it and then passing it to double again.

I'll try.

beowulf

I used QString::mid!

@qDebug() << QString::number(52.48).mid(QString::number(52.48).length() - 1, QString::number(52.48).length());@

And it's return the last number.

beowulf

Update

Maybe a little big, but that's the solution:

@qDebug() << QString::number(52.48).replace(QString::number(52.48).mid(QString::number(52.48).length() - 1, QString::number(52.48).length()), "");@

beowulf

Keep don't working.

The problem now is: 52.48 now is 5.4 with:

qDebug() << QString::number(52.48).replace(QString::number(52.48).mid(QString::number(52.48).length() - 1, QString::number(52.48).length()), "");

Jake007

Hi!

Why are you converting to string?

Multiply both numbers by the number of decimals and cast to int.
So
@auto a = (int)(52.4 * 10) // 524
auto b = (int)(52.48 * 10) // 524

if( a == b) // means that 52.4 equals 52.48
...
@

Further on, you can replace * 10 with pow(10, decimalPlaces) to have decimal place comparison dynamical.

If you want it back written as 52.4, just divide it by 10.

Regards,
Jake

beowulf

Wow, wow, wow, Thank you very much Jake007!

Jake007

You're welcome :) .
Don't forget to mark thread as solved.
And next time you're dealing only with numbers, please leave strings out of it.
Your processor will be grateful :)

Regards,
Jake