double floor(double x); float floor(float x); long double floor(long double x); double floor(T x); //为整型
floor()函数采用单个参数，并返回double，float或long double类型的值。此函数在<cmath>头文件中定义。
floor()函数采用一个参数，该参数的底值被计算。
floor()函数返回的最大可能整数值小于或等于给定参数。
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
double x = 10.25, result;
result = floor(x);
cout << "Floor of " << x << " = " << result << endl;
x = -34.251;
result = floor(x);
cout << "Floor of " << x << " = " << result << endl;
x = 0.71;
result = floor(x);
cout << "Floor of " << x << " = " << result << endl;
return 0;
}运行该程序时，输出为：
Floor of 10.25 = 10 Floor of -34.251 = -35 Floor of 0.71 = 0
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
int x = 15;
double result;
result = floor(x);
cout << "Floor of " << x << " = " << result << endl;
return 0;
}运行该程序时，输出为：
Floor of 15 = 15
整数值的下限就是整数值本身，所以实际中对整数值不使用下限函数。