/in/foo.c: In function 'main':
/in/foo.c:5:2: warning: implicit declaration of function 'gets' [-Wimplicit-function-declaration]
  gets(s1);
  ^~~~
/in/foo.c:18:2: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
  printf("%s\n",sresult);
  ^~~~~~
/in/foo.c:18:2: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:18:2: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:7:6: warning: unused variable 'len1' [-Wunused-variable]
  int len1=strlen(s1),len2=strlen(s2),len3=strlen(sresult);
      ^~~~
/tmp/ccDhhF52.o: In function `main':
foo.c:(.text.startup+0x1d): warning: the `gets' function is dangerous and should not be used.