C/C++ 取整函数ceil(),floor()

#include <math.h> double
floor(double x);

float floorf(float x);
long double floorl(long double x);

double floor(double x);
double ceil(double x);

使用floor函数。floor(x)返回的是小于或等于x的最大整数。

如： floor(10.5) == 10 floor(-10.5) == -11

使用ceil函数。ceil(x)返回的是大于x的最小整数。

如： ceil(10.5) == 11 ceil(-10.5) ==-10

floor()是向负无穷大舍入，floor(-10.5) == -11；

ceil()是向正无穷大舍入，ceil(-10.5) == -10

不得不说点：/ % 四舍五入 向上取整（ceil()） 向下取整（floor）

1. /

//Test "/"

cout << "Test \"/\"!" << endl;

cout << "7 / 2 = " << 7/2 << endl; //3

cout << "7 / 2.0 = " << 7/2.0 << endl; //3.5

cout << "7.0 / 2 = " << 7.0/2 << endl; //3.5

cout << "7.0 / 2.0 = " << 7.0/2.0 << endl; //3.5

cout << "7 / 3 = " << 7/3 << endl; //2

cout << endl;

2. %

//Test "%"

cout << "Test \"%\"!" << endl;

cout << "9 % 3 = " << 9%3 << endl; //0

cout << "9 % 4 = " << 9%4 << endl; //1

//cout << "9.0 % 3 = " << 9.0%3 << endl;

//cout << "9 % 3.0 = " << 9%3.0 << endl;

cout << endl;

3. 四舍五入

//Test round()

cout << "Test \"四舍五入\"!" << endl;

double dRoundA = 1.4;

double dRoundB = 1.6;

double dRoundLowA = -1.4;

double dRoundLowB = -1.6;

double dRoundLowC = 0.0;

cout << dRoundA << " = " << RoundEx(dRoundA) << endl; //1

cout << dRoundB << " = " << RoundEx(dRoundB) << endl; //2

cout << dRoundLowA << " = " << RoundEx(dRoundLowA) << endl; //-1

cout << dRoundLowB << " = " << RoundEx(dRoundLowB) << endl; //-2

cout << dRoundLowC << " = " << RoundEx(dRoundLowC) << endl; //0

cout << endl;

double RoundEx(const double& dInput)

{

double dIn = dInput;

if (dInput >= 0.0) //???

{

return int(dIn + 0.5);

}

else

{

return int(dIn - 0.5);

}

}

4. ceil() 向上取整

//Test ceil() 向上取整

cout << "Test ceil() 向上取整!" << endl;

cout << "ceil 1.2 = " << ceil(1.2) << endl; //2

cout << "ceil 1.8 = " << ceil(1.8) << endl; //2

cout << "ceil -1.2 = " << ceil(-1.2) << endl; //-1

cout << "ceil -1.8 = " << ceil(-1.8) << endl; //-1

cout << "ceil 0.0 = " << ceil(0.0) << endl; //0

cout << endl;

5. floor() 向下取整

//Test floor() 向下取整

cout << "Test floor() 向下取整!" << endl;

cout << "floor 1.2 = " << floor(1.2) << endl; //1

cout << "floor 1.8 = " << floor(1.8) << endl; //1

cout << "floor -1.2 = " << floor(-1.2) << endl; //-2

cout << "floor -1.8 = " << floor(-1.8) << endl; //-2

cout << "floor 0.0 = " << floor(0.0) << endl; //0

cout << endl;