#include <float.h>
#include <math.h>
#include <iostream>

using std::cout;
using std::endl;

int main()
{
	//判斷double值是否為0
	double dValue = 0.0;
	if (fabs(dValue) < DBL_EPSILON )
	{
		std::cout << "dValue的值為零" << std::endl;
	}
	else
	{
		std::cout << "dValue的值不為零" << std::endl;
	}

	double dValue0 = 1e-15;
	if (fabs(dValue0) < DBL_EPSILON)
	{
		std::cout << "dValue0的值為零" << std::endl;
	}
	else
	{
		std::cout << "dValue0的值不為零" << std::endl;
	}


	//C++/C科學計數法
	double scientificValue0 = 1e-2;   //0.01
	double scientificValue1 = 1e3;     //1000
	cout << scientificValue0 << endl
		<< scientificValue1 <<endl;

	system("pause");

	return 0;
}
 

引用一句話：

         再也不用睜大眼睛去數有多少零了。