求平方根C++

   求平方根,正根.曾经都不会.昨天看数学,看到了,写了出来.自己又小优化了一下,非常不错.

// squareRoot.cpp -- 2011-08-29-01.04

#include "stdafx.h"

#include <iostream>



double squareRoot (double radicand, double precision) ;



int _tmain(int argc, _TCHAR* argv[])

{

	std ::cout << squareRoot(9, 0.000001) << std ::endl ;



	return 0;

}



double squareRoot (double radicand, double precision)

{

	if (radicand > 0)

	{

		double squareRoot = radicand / 10 ;

		while (squareRoot * squareRoot > radicand)

			squareRoot /= 2 ;

		double fakePrecision = 0.1; 

		while (1)

		{

			while ((squareRoot + fakePrecision) * (squareRoot + fakePrecision) <= radicand)

			{

				squareRoot += fakePrecision ;

			}

			if (fakePrecision > precision)

			{

				fakePrecision /= 10 ;

			}

			else

			{

				return squareRoot ;

			}

		}

	}

	else

	{

		std ::cerr << "Radicand must > 0" << std ::endl ;

		return 0 ;

	}

}