为啥用const pi=3.1415926后pi输出的是3.14159

#include
#include
using namespace std;
int main()
{
double radius;
double const pi=3.1415926;
double a;
cout<<"输入圆的半径:";
cin>>radius;
a=piradiusradius;
cout<<"圆周率为："<<setw(10)<<pi<<endl;
cout<<"半径为："<<setw(10)<<radius<<endl;
cout<<"圆的面积为；"<<setw(10)<<a<<endl;
}

c++中不做任何操作，默认情况下只显示6六位数据

供参考：C++中cout用法https://blog.csdn.net/weixin_45595778/article/details/104620044?ops_request_misc=&request_id=&biz_id=102&utm_term=c++%E4%B8%AD%20cout%E7%94%A8%E6%B3%95%E8%AF%A6%E8%A7%A3&utm_medium=distribute.pc_search_result.none-task-blog-2~all~sobaiduweb~default-0-104620044.first_rank_v2_pc_rank_v29&spm=1018.2226.3001.4187