foo.cc:4:9: error: conversion from ‘double’ to ‘long unsigned int’ in a converted constant expression
    4 | int n,p[M];
      |         ^
foo.cc:4:9: error: could not convert ‘M’ from ‘const double’ to ‘long unsigned int’
    4 | int n,p[M];
      |         ^
      |         |
      |         const double
foo.cc:4:9: error: size of array ‘p’ has non-integral type ‘const double’