/in/foo.c: In function 'main':
/in/foo.c:7:29: error: 'o' undeclared (first use in this function)
    7 |         int term = 0, sum = o;
      |                             ^
/in/foo.c:7:29: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:14:9: error: 'returno' undeclared (first use in this function)
   14 |         returno;
      |         ^~~~~~~