foo.cc: In function 'void finds(int, int, int, int)':
foo.cc:10:34: error: 's' was not declared in this scope
  if(xs==xe&&ys==ye) {printf("%c",s[xs]);return;}
                                  ^
foo.cc:10:34: note: suggested alternative: 'xs'
  if(xs==xe&&ys==ye) {printf("%c",s[xs]);return;}
                                  ^
                                  xs
foo.cc:15:14: error: 's' was not declared in this scope
  printf("%c",s[t]);
              ^
foo.cc: In function 'int main()':
foo.cc:23:2: error: 'l' was not declared in this scope
  l=strlen(s1);
  ^
foo.cc:21:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s",s1);
  ~~~~~^~~~~~~~~
foo.cc:22:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s",s2);
  ~~~~~^~~~~~~~~

自豪的采用 HydroJudge 进行评测(github.com/hydro-dev/HydroJudge)