convert string (an equation) to float

Programming Questions

yeney_leo

convert string (an equation) to float

in Programming Questions • 1 year ago

here I got a question in processing.org,
if I wrote:

float result= 1+3*5;
println(result);

I will get 16;

but the input here I have is the string="1+3*5";
float result = string;
it will occour an error,

I tried the following:

float f = Float.valueOf(str).floatValue();
or
float f = new Float(str);

but they don't work.

anyone knows how to solve that?
Great Thanks,
Leo

Replies(8)

calsign

Re: convert string (an equation) to float

1 year ago

Java is compiled, not interpreted.
This question has been asked many times before...

For example, this thread.

yeney_leo

Re: convert string (an equation) to float

1 year ago

sorry...
I am a noob here, first time lerning programme....
I cannot change what I get from somewhere else. it is a string equation that i got.

calsign

Re: convert string (an equation) to float

1 year ago

It is really difficult to compile a String in the way that you want, although not impossible.
If you want to try that, I would suggest looking at BeanShell.
Do you have to compute a String given to you?

yeney_leo

Re: Re: convert string (an equation) to float

1 year ago

I have the equation input somewhere else, and transmitted from COM port, it is a string here.
and in processing, I use

myString = myPort.readStringUntil('=');

to read out the string.
say it is 1+3*5;
in this processing,I want to calculate the result.
that's what I want this program to do.....

I know the method called stack. but in process there is no stack.
By the way, really thanks for your patience....

PhiLho

Re: convert string (an equation) to float

1 year ago

In the recent past, I shown how to use the JavaScript interpreter shipped with Java to interpret such kind of equation. Perhaps a search will dig out this thread.

yeney_leo

Re: Re: convert string (an equation) to float

1 year ago

https://forum.processing.org/topic/executing-a-string-or-other-procedure-for-a-calculator
do you mean this one?
I read that. and don't understand....

PhiLho

Re: convert string (an equation) to float

1 year ago

No, this one: https://forum.processing.org/topic/execute-a-string
I show several ways to do it, you have to choose only one...

yeney_leo

Re: Re: convert string (an equation) to float

1 year ago

thank you indeed, the calculation is simple, so I use the first method.and it works!

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;

String myString="1+7-15%2";
void setup() {
float result= xmain();
println(result);
}

float xmain() {
float result=0f;
ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("javascript");

try {
    String jsCode = "importPackage(java.util); var xxx ="+myString+" ; \n";
    engine.eval(jsCode);
    result=(Float)engine.get("xxx");

}
catch (Exception e) {
    e.printStackTrace();
}
return result;
}