/in/foo.cc: In function 'bool flag(char*, char*)':
/in/foo.cc:8:5: error: 'strrev' was not declared in this scope; did you mean 'strsep'?
    8 |     strrev(b);
      |     ^~~~~~
      |     strsep
/in/foo.cc:7:9: warning: unused variable 'lena' [-Wunused-variable]
    7 |     int lena=strlen(a);
      |         ^~~~