幂函数
求x的y次幂
double pow(double x,double y);
求x的0.5次幂也就是根号x
double sqrt(double x);
double x = pow(2,3); //求2的三次方
doueble x = pow(2,0.5); //求根号2
double x = sqrt(5); //求根号5，作用与上面那个类似三角函数
cos(x)：x的余弦值
double cos(double x);
tan(x)：x的正切值
double tan(double x);
asin(x)：x的反正弦值
double asin(double x);
acos(x)：x的反余弦值
double acos(double x);
atan(x)：x的反正切值
double atan(double x);对数函数
exp(x)：指数函数 e^x，e ≈ 2.718
double exp(double x);
log(x)：自然对数函数 ln(x)，x > 0
double log(double x);
log10(x)：以10为底的对数log10(x)，x > 0
double log10(double x);取整函数
ceil(x)：向上取整，即不小于x的最小整数
double ceil(double x);
round(x)：四舍五入
double round(double x);
floor(x)：向下取整，即不大于x的最大整数
double floor(double x);
double x = 10.5;
cout << ceil(x) << endl; //11
cout << round(x) << endl; //11
cout << floor(x) << endl; //10绝对值
fabs(x)：x的绝对值
double fabs(double x);其他
fmod(x, y)：x/y的浮点余数
double fmod(double x,double y);
double x = fmod(10.5, 5); // x = 0.5
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