foo.cc: In function ‘int fac(int)’:
foo.cc:7:9: error: expected ‘,’ or ‘;’ before ‘for’
    7 |         for(int i=1;i<=n;i++)
      |         ^~~
foo.cc:7:21: error: ‘i’ was not declared in this scope
    7 |         for(int i=1;i<=n;i++)
      |                     ^