Compilare: user.c: In function ‘add’: user.c:16:5: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration] GRAPH *p = (GRAPH*) malloc (sizeof (GRAPH)); ^ user.c:16:25: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] GRAPH *p = (GRAPH*) malloc (sizeof (GRAPH)); ^ user.c: In function ‘read’: user.c:26:11: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d%d", &n, &m); ^ user.c:29:15: warning: ignoring return value of ‘scanf’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d%d", &edge1, &edge2); ^ user.c: In function ‘main’: user.c:47:13: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen (IN, "r", stdin); ^ user.c:48:13: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result] freopen (OUT, "w", stdout); ^