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Index › Programming Questions & Help › Syntax Questions › Anyone know how to build a calculator
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Anyone know how to build a calculator? (Read 788 times)
leRiCl
Anyone know how to build a calculator?
Feb 5th, 2007, 2:09pm  
I am trying to create a graph program with creates graphs based on the equations you enter.  (More Specifically, graph complex numbers on the argand diagram, and I think it shouldn't be much harder than normal graphs if you treat i just as any other variable) Naturally, I'd need a built in calculator. I've finished the GUI side of the program, its just the guts I need. As you can see my attempt, it is pathetic. It cannot handle variables, just numbers. There is no order of operation either, so 1+2*2+1=7... Please give some tips.

Code:

void ParseString()
{
  String side[]=split(StringEdit,'='); 
  //LHS and RHS
  int Mdlvl;
  int Ptlvl;
  float Number=0;
  
  int mode=1;// 1=add,2=sub,3=multi,4=div;
  int dec;//1 - dec, 2= no


  int nI;
  int nX;
  int nY;

  //Lets do linear first
  int NRadians;
  int distance;
  String tempnumber="";
  for (int i=0;i<side[1].length();i++)
  {
    if (side[1].charAt(i)=='1' || side[1].charAt(i)=='2' || side[1].charAt(i)=='3' || side[1].charAt(i)=='4' || side[1].charAt(i)=='5' || side[1].charAt(i)=='6' || side[1].charAt(i)=='7' || side[1].charAt(i)=='8' || side[1].charAt(i)=='9' || side[1].charAt(i)=='0' || side[1].charAt(i)=='.')
    {
	tempnumber=tempnumber+side[1].charAt(i);
    }

    if ((side[1].charAt(i)=='/') ||(side[1].charAt(i)=='+') || (side[1].charAt(i)=='-')|| (side[1].charAt(i)=='*') || i==side[1].length()-1)
    {
	if (mode==1)
	{
	  Number=Number+float(tempnumber);
	  tempnumber="";
	}
	if (mode==2)
	{
	  Number=Number-float(tempnumber);
	  tempnumber="";
	}
	if (mode==3)
	{
	  Number=Number*float(tempnumber);
	  tempnumber="";
	}
	if (mode==4)
	{
	  Number=Number/float(tempnumber);
	  tempnumber="";
	}
    }


    if (side[1].charAt(i)=='+')
    {
	mode=1;
    }
    if (side[1].charAt(i)=='-')
    {
	mode=2;
    }
    if (side[1].charAt(i)=='*')
    {
	mode=3;
    }
    if (side[1].charAt(i)=='/')
    {
	mode=4;
    }



  }
  println (Number);
}
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st33d
Re: Anyone know how to build a calculator?
Reply #1 - Feb 5th, 2007, 5:24pm  
Most useful equations tend to be a transformation. You would plot f(x) to get y. You know where x is, but you run it through f() to get y.

I put some useful graphs like sigmoid transformation and normal distribution (bell curve) here on Seltar's Snippets.

You should model your operator precedence on the Java standard, so as not to confuse yourself.

http://www.uni-bonn.de/~manfear/javaoperators.php

Considering that you're doing some quite difficult string operations I would recommend performing the task using regular expressions.

http://java.sun.com/docs/books/tutorial/essential/regex/

They're hard to get into, but once you've sat down and played with it for an hour or so you find that you can turn ten lines of Java code into one regex. You can perform matches, replacements and other operations quickly and you can take this skill into other languages (I like Perl me).

Good luck.
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