Compilare: user.c: In function ‘main’: user.c:44:9: warning: implicit declaration of function ‘abs’ [-Wimplicit-function-declaration] a[dr] = abs(l[i] - l[j]); ^ user.c:26:9: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(in, "%d", &n); ^ user.c:29:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(in, "%d%d", &l[i], &c[i]); ^