Compilare: user.c: In function ‘main’: user.c:29:5: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration] char *sieve = (char*)malloc(CHARS * sizeof(char)); ^ user.c:29:26: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] char *sieve = (char*)malloc(CHARS * sizeof(char)); ^