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【Java】利用正则表达式和string制作计算器

作者:shany33 / 发布于2015/9/14/ 697

首先我用string来储存数字，使得支持大数，并且将负数以最高位添加0来表示（会增加判断数字正负的困难，如：0.1是正数，00.1才是负数），并且自己编写了string数字的运算，有加减乘除、取模、开根号、幂运算、正余弦、e^x、阶乘，并且支持多重括号改变运算优先级。


	string expression(str);
	 string pattern = "(\\()([-])([0-9]+)([.][0-9]+)?(\\))"; //find(-15)or(-15.02),and transform it into -15 or -15.02
	 regex r(pattern);
	 string format = "0$3$4";
	
	 expression = regex_replace(expression, r, format);
	 //cout << expression << endl;
	
	 pattern = "(\\()([0-9]+)([.][0-9]+)?(\\))"; //find(15)or(15.02),and transform it to 15 or 15.02
	 r.assign(pattern);
	 format = "$2$3";
	
	 expression = regex_replace(expression, r, format);
	 //cout << expression << endl;
	
	 pattern = "(s)([0-9]+)([.][0-9]+)?"; //find s(x), and calculate it as sin(x)
	 r.assign(pattern);
	 while (regex_search(expression, result, r))
	 {
	 temp = result.str(2) + result.str(3);
	 product = sin(temp);
	 expression = result.prefix().str() + product + result.suffix().str();
	 }
	
	
	 pattern = "(c)([0-9]+)([.][0-9]+)?"; //find c(x), and calculate it as cos(x)
	 r.assign(pattern);
	 while (regex_search(expression, result, r))
	 {
	 temp = result.str(2) + result.str(3);
	 product = cos(temp);
	 expression = result.prefix().str() + product + result.suffix().str();
	 }
	
	
	 pattern = "(e)([0-9]+)([.][0-9]+)?"; //find e(x), and calculate it as Exp(x)
	 r.assign(pattern);
	 while (regex_search(expression, result, r))
	 {
	 temp = result.str(2) + result.str(3);
	 product = Exp(temp);
	 expression = result.prefix().str() + product + result.suffix().str();
	 }
	
	
	 pattern = "([0-9]+)([.][0-9]+)?(!)"; //find (x)!, and calculate it as factorial(x)
	 r.assign(pattern);
	 while (regex_search(expression, result, r))
	 {
	 if (result.str(2) != "")
	 {
	 cerr << "invalid expression of " << result.str() << "!";
	 exit(1);
	 }
	 temp = result.str(1);
	 product = factorial(temp);
	 expression = result.prefix().str() + product + result.suffix().str();
	 }
	
	
	 pattern = "(\\()([0-9]+)([.][0-9]+)?([-+/*%#^]([0-9]+)([.][0-9]+)?)+(\\))"; //find the compound expression in the ( )
	
	 r.assign(pattern);
	
	 while (regex_search(expression, result, r))//inside start

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