/in/foo.c: In function 'bub':
/in/foo.c:5:23: error: 'l' undeclared (first use in this function)
    5 |         for(int i=0;i<l-1;i++){
      |                       ^
/in/foo.c:5:23: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:4:5: warning: unused variable 'len' [-Wunused-variable]
    4 | int len=strlen(s);
      |     ^~~