/in/foo.c: In function 'main':
/in/foo.c:9:10: error: expected expression before 'for'
    9 |         -for(i=1;i<a;i++)
      |          ^~~
/in/foo.c:5:15: warning: variable 'sum' set but not used [-Wunused-but-set-variable]
    5 |     int a,n,i,sum;
      |               ^~~
/in/foo.c:5:13: warning: unused variable 'i' [-Wunused-variable]
    5 |     int a,n,i,sum;
      |             ^