foo.c: In function 'main':
foo.c:7:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s1);
  ^~~~
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__;
              ^~~~
foo.c:8:2: warning: 'gets' is deprecated [-Wdeprecated-declarations]
  gets(s2);
  ^~~~
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__;
              ^~~~
foo.c: In function 'Diff':
foo.c:15:24: warning: unused variable 'j' [-Wunused-variable]
  int c=0,m=0,C=0,M=0,i,j;
                        ^
foo.c:15:18: warning: unused variable 'M' [-Wunused-variable]
  int c=0,m=0,C=0,M=0,i,j;
                  ^
foo.c:15:14: warning: unused variable 'C' [-Wunused-variable]
  int c=0,m=0,C=0,M=0,i,j;
              ^
/tmp/ccv0Cs7W.o: In function `main':
foo.c:(.text.startup+0x15): 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)