Correcting data by equation parameters

[erytcg]

Hello I have some data in my program and I want correct it.
For example:
x = 1,012;

I need command line where I could enter some like this:

x=0.98*x+0.1;
or like this
x=(1.3x+1)^2;

with the mathematic sequence of actions

[SGaist]

Hi,

What do you mean by "command line" ?

[erytcg]

Maybe QLineEdit it doesn't matter, widget to input String.

[SGaist]

Are you looking to implement something like SpeedCrunch ?

[erytcg]

I need something simple. Maybe only y=ax+b;

[mrjj]

@erytcg
and you want to parse it and execute it ?
There are many examples of a small calculator on the net. its a common
text book task.

[VRonin]

https://en.wikipedia.org/wiki/Shunting-yard_algorithm

[erytcg]

any example for calculating without buttons? only input line.

[mrjj]

@erytcg
The link VRonin gave is without buttons.
Just the pure way to do it.

[erytcg]

It is possible to use varibales names in this?

[mrjj]

@erytcg
yeah should be as you can just treat the variable as a number and substitute when you calculate the result.
it also support operator precedence but stuff like
x=(1.3x+1)^2;
will require somewhat a more data complex model to handle flawless i think.

[erytcg]

And one more question this algorithm is fast? I have a looot of data and I have to calculate it in real time:D

[mrjj]

@erytcg
well, it's minimal and makes handling the expressions easier (for the programmer) but since it is sort of a text parser, not that fast but for small expressions its not wildly time consuming.

[mrjj]

Depending on what you need to handle, maybe using something like
https://github.com/ArashPartow/exprtk ?

[erytcg]

Can I use QScriptEngine?

But I have problem

#include <QtScript/qscriptengine.h>
#include <QtScript/qscriptvalue.h>

QString x = ui->correctDataLine->displayText();
QScriptEngine myEngine;
QScriptValue x2 = myEngine.evaluate(x);
qDebug() << x2.toNumber();

undefined reference to `_imp___ZN13QScriptEngineC1Ev'

[mrjj]

@erytcg
do you have
QT += script
in the pro file?

[erytcg]

Ok thanks my bad:(
Do you think can I use this with variables names?

[mrjj]

@erytcg
What do you mean with "variables names" ?
To put inside QScriptEngine or what you wanna do with variables?

[mrjj]

Ah I see where you are aiming :)
Yes you can use it for your use case. Depending on the complexity you need.
http://www.informit.com/articles/article.aspx?p=1405559&seqNum=2
Using script with js to play calculator.

[erytcg]

I have this

And I have variable name: x. I put to QLineEdit 1+x * 3
And script automatically calculate new value of x.
x = 1+x*3