Compilare: user.c: In function ‘disjoint_set_new’: user.c:56:5: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration] disjoint_set* forest = malloc( sizeof(disjoint_set) ); ^ user.c:56:28: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] disjoint_set* forest = malloc( sizeof(disjoint_set) ); ^