atan2&sin

//弧度转化角度：弧度*180/PI
//角度转化弧度：角度*PI/180

#include <math.h> 
#include <stdio.h> 
const double PI=acos(-1.0); 
//sin传入的参数的是弧度
void main() 
{ 
    int z=30;
    double   x   =   10.0,   y   =   10.0;     
    double   result;     
    //sin30结果
    printf("sin(%d)=%.2lf
",z,sin(2*PI*z/360.0)); 
    result=atan2(y,   x);     //结果返回是弧度
    printf("The   arc   tangent   ratio   of   %lf   is   %.1lf
",   (y   /   x),   result*180/PI);  
    //sin45的结果
    printf("sin(%.0f)=%.2lf
",result*180/PI,sin(result));    //注意不要用%d
}