That is a little vague. What type of calculator exactly? A GUI one, or just an expression parser&#x2F;evaluator? For the latter, you might find this interesting:<p><a href="http:&#x2F;&#x2F;www.hugi.scene.org&#x2F;compo&#x2F;compoold.htm#compo4" rel="nofollow">http:&#x2F;&#x2F;www.hugi.scene.org&#x2F;compo&#x2F;compoold.htm#compo4</a>