Calculator

Hi there,
I'm fairly new to Java and was going to program a calculator whereby the input is entered in a single expression (e.g 4 + 3 * 5) rather than asking for the first integer, then an operator, then second integer etc.
I also want the program to do the math in the correct order such that multiplication is before addition and so on.
However, i've had a 2-3 week break from programming during the Christmas period so I have just come across a complete mental block of how I would even go about starting this calculator.
I have read about a scanner class which could be used but I have never used it myself before so would this be useful?
Any help is greatly apprectiated, thanks :)

I wrote a blog article for this forum on an (infix) expression compiler once; its source code is free of use; (see the link at the right side of this reply).

kind regards,

Jos

Thanks, but the sample code at the bottom of the blog no longer works :(

Quote:

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Originally Posted by Elviii

Thanks, but the sample code at the bottom of the blog no longer works :(

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Strange, I just gave it a try and it works fine for me ... I'll try to attach the .zip file here ... hm, strange; the attachment facility seems to be broken; I'll see if it can be fixed.

kind regards,

Jos

I get this message:

vBulletin Message
Invalid Attachment specified. If you followed a valid link, please notify the administrator

That's exactly what I'm going to do ;-) I don't have any facilities to fix it myself (thank god)

kind regards,

Jos

You could use the Shunting Yard Algorithm to parse your expression.

Shunting-yard algorithm - Wikipedia, the free encyclopedia

To tokenize your expression, you could use Java's StringTokenizer class.

StringTokenizer tokenizer = StringTokenizer(expression, delimiters, true);

Your operators could be the delimiters.

You would then call tokenizer.nextToken() to get each token of the expression.

Anyway, that would take some work, but it would work.