/in/foo.cc: In function 'int main()':
/in/foo.cc:9:62: warning: left operand of comma operator has no effect [-Wunused-value]
    9 |                 for (int j=ceil(xb*1.0/2),i=floor(xb*1.0/2);i>=num/5,j<=num/2;i--,j++)
      |                                                             ~^~~~~~~