Convert String to math equation?

Question

I'm trying to figure out how to parse an input string that contains a math equation given by the user like 2x^2+3x+6 to a double that operates the String with its variables that I will define later on with a for loop.

Basically,

for(x=0;x<=100;x++){
    String equation = "2x^2+3x+6";
    double y = equation;
    System.out.println("Your point is x: " + x +" | Y: " + y);
}

I found this old post but the BeanSheel Library only allowed me to use actual numbers without parameters like "x".

So what I'm trying to achieve is a program that will draw a function given by the user. But for the drawing part I'm fine

The answer will depend on the language, which you have failed to specify. — Scott Hunter, Jan 23 '17 at 18:53
Sorry, i'm new to posting questions, it's java, how do i specify it in the post? Thanks — David Millán, Jan 23 '17 at 18:55
we try to solve this problem in our `compiler` course , we made a parse table from possible rules , then read our input file , and try to generate codes that refers to our math equation — Mohsen_Fatemi, Jan 23 '17 at 18:56
but you only want to have the answer of equation , it is not neccessary to learn about compilers — Mohsen_Fatemi, Jan 23 '17 at 18:58
You will have to write a parser to convert it to a function then evaluate the function for different values of x and plot the results. — Guy Coder, Jan 23 '17 at 19:08
Of interest: [JEval](http://jeval.sourceforge.net/) I have not used this but appears to have what you need. — Guy Coder, Jan 23 '17 at 19:11
Of interst: [GitHub - darius/expr](https://github.com/darius/expr) — Guy Coder, Jan 23 '17 at 19:14

score 0 · Answer 1 · answered Jan 23 '17 at 19:10

0

You could replace every occurrence of x within the equation string with the string representation of x's value; then you could use the post you linked to to evaluate it.

answered Jan 23 '17 at 19:10

Scott Hunter

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excuse me , i have a question , for this problem there are two solutions , 1- using `replace` method 2-`split` and rebuild the String using Stringbuilder , which one is efficient ? – Mohsen_Fatemi Jan 23 '17 at 19:15
Try both and see. I'd be worried about getting it to work first. – Scott Hunter Jan 23 '17 at 20:36

Convert String to math equation?

1 Answers1