C++保留小数点后两位(floor&ceil&round)详解

#include 
using namespace std;
int main()
{
	double i = 2.235687;
	double j = round(i * 100) / 100;
	cout << "The original number is "  << i << endl;
	cout << "The keep two decimal of 2.235687 is "  << j << endl;
	system("pause");
	return 0;
}

功能：把一个小数向下取整
      即就是如果数是2.2，那向下取整的结果就为2.000000
原型：double floor(doube x);
    参数解释：
        x:是需要计算的数

#include 
using namespace std;
int main()
{
    double i = floor(2.2);
    double j = floor(-2.2);
    cout << "The floor of 2.2 is " << i << endl;
    cout << "The floor of -2.2 is " << j << endl;
    system("pause");
    return 0;
}

功能：把一个小数向上取整
      即就是如果数是2.2，那向下取整的结果就为3.000000
原型：double ceil(doube x);
    参数解释：
        x:是需要计算的数

#include 
using namespace std;
int main()
{
    double i = ceil(2.2);
    double j = ceil(-2.2);
    cout << "The ceil of 2.2 is " << i << endl;
    cout << "The ceil of -2.2 is " << j << endl;
    system("pause");
    return 0;
}

功能：把一个小数四舍五入
      即就是如果数是2.2，那向下取整的结果就为2
                 如果数是2.5，那向上取整的结果就为3
原型：double round(doube x);
    参数解释：
        x:是需要计算的数

#include 
using namespace std;
int main()
{
    double i = round(2.2);
    double x = round(2.7);
    double j = round(-2.2);
    double y = round(-2.7);
    cout << "The round of 2.2 is " << i << endl;
    cout << "The round of 2.7 is " << x << endl;
    cout << "The round of -2.2 is " << j << endl;
    cout << "The round of -2.7 is " << y << endl;
    system("pause");
    return 0;
}