/in/foo.c: In function 'main':
/in/foo.c:17:5: warning: implicit declaration of function 'memset' [-Wimplicit-function-declaration]
     memset(f, 0, sizeof(f));
     ^~~~~~
/in/foo.c:17:5: warning: incompatible implicit declaration of built-in function 'memset'
/in/foo.c:17:5: note: include '<string.h>' or provide a declaration of 'memset'