foo.cpp: In function 'double solve(int)':
foo.cpp:62:15: warning: 'mid' may be used uninitialized in this function [-Wmaybe-uninitialized]
  double p = (a+b+c)/2.0;
              ~^~
foo.cpp:75:21: note: 'mid' was declared here
  double begin, end, mid;
                     ^~~