foo.c: In function 'main':
foo.c:7:18: warning: initialization makes integer from pointer without a cast [-Wint-conversion]
 char str[100] = {NULL};//定义删除前的字符串
                  ^~~~
foo.c:7:18: note: (near initialization for 'str[0]')
foo.c:8:17: warning: initialization makes integer from pointer without a cast [-Wint-conversion]
 char st[100] = {NULL};//定义删除后的字符串
                 ^~~~
foo.c:8:17: note: (near initialization for 'st[0]')
foo.c:11:1: warning: 'gets' is deprecated [-Wdeprecated-declarations]
 gets(str);//输入字符串
 ^~~~
In file included from foo.c:1:0:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/tmp/cceGT0DO.o: In function `main':
foo.c:(.text.startup+0x36): warning: the `gets' function is dangerous and should not be used.

自豪的采用jd5进行评测(github.com/masnn/jd5)