Warning(s):

source_file.c: In function ‘main’:
source_file.c:6:8: warning: initialization makes integer from pointer without a cast [-Wint-conversion]
 char c=NULL;
        ^
source_file.c:7:2: warning: assignment makes integer from pointer without a cast [-Wint-conversion]
 c="hogehoge";
  ^
source_file.c:6:6: warning: variable ‘c’ set but not used [-Wunused-but-set-variable]
 char c=NULL;
      ^