#1 make gives warnings about declaration

[Anonymous]

$ make
gcc -o ciso.o -c ciso.c
ciso.c: In function 'check_file_size':
ciso.c:56: warning: incompatible implicit declaration of built-in function 'memset'
ciso.c: In function 'decomp_ciso':
ciso.c:130: warning: incompatible implicit declaration of built-in function 'memset'
ciso.c:194: warning: incompatible implicit declaration of built-in function 'memcpy'
ciso.c: In function 'comp_ciso':
ciso.c:271: warning: incompatible implicit declaration of built-in function 'memset'
ciso.c:361: warning: incompatible implicit declaration of built-in function 'memcpy'
gcc -o ciso ciso.o -lz

Just adding #include <string.h> to ciso.c looks like it fixes the problem.
After adding the line I do not get warnings with make.