/in/foo.c: In function 'AB':
/in/foo.c:9:14: warning: comparison between pointer and integer
  while (B[j] == "") {
              ^~
/in/foo.c:9:14: warning: comparison with string literal results in unspecified behavior [-Waddress]
/in/foo.c:14:9: warning: return makes integer from pointer without a cast [-Wint-conversion]
  return A;
         ^
/in/foo.c: In function 'BA':
/in/foo.c:22:14: warning: comparison between pointer and integer
  while (A[j] == "") {
              ^~
/in/foo.c:22:14: warning: comparison with string literal results in unspecified behavior [-Waddress]
/in/foo.c:27:9: warning: return makes integer from pointer without a cast [-Wint-conversion]
  return B;
         ^
/in/foo.c: In function 'main':
/in/foo.c:43:2: warning: implicit declaration of function 'system' [-Wimplicit-function-declaration]
  system("pause");
  ^~~~~~