/in/foo.c: In function 'main':
/in/foo.c:5:2: warning: implicit declaration of function 'gets' [-Wimplicit-function-declaration]
  gets(a);
  ^~~~
/in/foo.c:6:2: warning: implicit declaration of function 'strcpy' [-Wimplicit-function-declaration]
  strcpy(b,a);
  ^~~~~~
/in/foo.c:6:2: warning: incompatible implicit declaration of built-in function 'strcpy'
/in/foo.c:6:2: note: include '<string.h>' or provide a declaration of 'strcpy'
/in/foo.c:40:3: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   printf("0");
   ^~~~~~
/in/foo.c:40:3: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:40:3: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:42:2: warning: implicit declaration of function 'puts' [-Wimplicit-function-declaration]
  puts(b);
  ^~~~
/tmp/ccketn1F.o: In function `main':
foo.c:(.text.startup+0x10): warning: the `gets' function is dangerous and should not be used.