math.h中的常量

类似于Matlab中经常用到的一些常量，C++里边也是有的。（经查源文件无意中看到）
写入如下代码：

 #include<iostream>
 #include<iomanip>
 #define _USE_MATH_DEFINES
 #include<math.h>
 using namespace std;
 int main()
 {
 system("color 3e");
 int a=;
 cout<<setprecision();
 cout<<"e          "<<M_E<<endl;
 cout<<"log2(e)    "<<M_LOG2E<<endl;
 cout<<"log10(e)   "<<M_LOG10E<<endl;
 cout<<"ln(2)      "<<M_LN2<<endl;
 cout<<"ln(10)     "<<M_LN10<<endl;
 cout<<"pi         "<<M_PI<<endl;
 cout<<"1/pi       "<<M_1_PI<<endl;
 cout<<"2/pi       "<<M_2_PI<<endl;
 cout<<"pi/2       "<<M_PI_2<<endl;
 cout<<"pi/4       "<<M_PI_4<<endl;
 cout<<"sqrt(2)    "<<M_SQRT2<<endl;
 cout<<"1/sqrt(2)  "<<M_SQRT1_2<<endl;
 cout<<"2/sqrt(pi) "<<M_2_SQRTPI<<endl;
 cout<<"八进制：   "<<oct<<a<<endl;
 cout<<"十进制：   "<<dec<<a<<endl;
 cout<<"十六进制： "<<hex<<a<<endl;
 cout<<"八进制：   "<<setbase()<<a<<endl;
 cout<<"十进制：   "<<setbase()<<a<<endl;
 cout<<"十六进制： "<<setbase()<<a<<endl;
 return ;
 }