Compilare: user.c: In function ‘main’: user.c:17:5: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration] int *sieve = (int*)malloc((B + 1) * sizeof(int)); ^ user.c:17:24: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] int *sieve = (int*)malloc((B + 1) * sizeof(int)); ^