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

[mrjj]

@erytcg
Only if you program in js to solve it. it can evaluate values for you but
it cant tell you what x is as far as i know.

[VRonin]

Why are you using JS libraries with a deprecated Qt module when @mrjj linked a good C++ library that can do what you want? there are even examples that do basically what you want to do.

If you want something that would solve generic expressions (i.e. no numeric values involved). The issue becomes a lot more complicated and, you are probably better off using a service like Wolfram Alpha's API