/in/foo.c: In function 'main':
/in/foo.c:11:15: warning: implicit declaration of function 'strlen' [-Wimplicit-function-declaration]
     int len = strlen(buf);
               ^~~~~~
/in/foo.c:11:15: warning: incompatible implicit declaration of built-in function 'strlen'
/in/foo.c:11:15: note: include '<string.h>' or provide a declaration of 'strlen'
/in/foo.c:17:13: warning: implicit declaration of function 'memcpy' [-Wimplicit-function-declaration]
             memcpy(&buf[i], &buf[i+1], len - i);
             ^~~~~~
/in/foo.c:17:13: warning: incompatible implicit declaration of built-in function 'memcpy'
/in/foo.c:17:13: note: include '<string.h>' or provide a declaration of 'memcpy'