自己写控制浮点数显示位数

                       C++中浮点数的显示很简单（默认显示小数点后5位且四舍五入），cout << fixed <<setPRecision(7) << area << endl;//小数点后面7位

                     但我想自己实现setprecision(7)函数，于是有如下代码：

#include<iostream>#include<iomanip>using namespace std;int main()//输出显示7位小数{	double number = 3.14159263358979323;	int lastnum = 0;	lastnum = ((int)(number * 100000000)) % 10;//小数点后面第8个数字	cout << lastnum << endl;	//四舍五入	if (lastnum >= 0 && lastnum <= 4)		number = ((int)(number * 10000000))*0.0000001;//第8位该舍	else if (lastnum >= 5 && lastnum <= 9)	{		number = (((int)(number * 10000000))*0.0000001) + 0.0000001;//第8位该入	}	cout << fixed << setprecision(7) << number << endl;	system("pause");	return(0);}