foo.cc: In function 'int main()':
foo.cc:9:11: warning: right operand of comma operator has no effect [-Wunused-value]
    9 |  for(i=2,i<n,i++)
      |          ~^~
foo.cc:9:17: error: expected ';' before ')' token
    9 |  for(i=2,i<n,i++)
      |                 ^
      |                 ;
foo.cc:16:2: error: expected primary-expression before 'if'
   16 |  if(i==n)
      |  ^~
foo.cc:15:3: error: expected ';' before 'if'
   15 |  }
      |   ^
      |   ;
   16 |  if(i==n)
      |  ~~
foo.cc:16:2: error: expected primary-expression before 'if'
   16 |  if(i==n)
      |  ^~
foo.cc:15:3: error: expected ')' before 'if'
   15 |  }
      |   ^
      |   )
   16 |  if(i==n)
      |  ~~
foo.cc:9:5: note: to match this '('
    9 |  for(i=2,i<n,i++)
      |     ^

[Hydro](https://hydro.ac)提供评测服务