/in/foo.cc:31:2: warning: "/*" within comment [-Wcomment]
  /*
   
/in/foo.cc: In function 'void add(int*, int)':
/in/foo.cc:62:6: warning: unused variable 'x' [-Wunused-variable]
  int x=1;
      ^
/in/foo.cc: In function 'void chengfa(int*, int*, int*, int, int)':
/in/foo.cc:81:21: warning: 'sizeof' on array function parameter 'c' will return size of 'int*' [-Wsizeof-array-argument]
  memset(c,0,sizeof(c));
                     ^
/in/foo.cc:79:36: note: declared here
 void chengfa(int a[],int b[],int c[],int lena,int lenb){
                                    ^
/in/foo.cc:81:19: warning: argument to 'sizeof' in 'void* memset(void*, int, size_t)' call is the same expression as the destination; did you mean to dereference it? [-Wsizeof-pointer-memaccess]
  memset(c,0,sizeof(c));
                   ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:178:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s);
        ^
In file included from /usr/include/c++/7/cstdio:42:0,
                 from /in/foo.cc:1:
/usr/include/stdio.h:640:14: note: declared here
 extern char *gets (char *__s) __wur __attribute_deprecated__;
              ^~~~
/tmp/ccXq3inR.o: In function `main':
foo.cc:(.text.startup+0x1a): warning: the `gets' function is dangerous and should not be used.