Compilare: user.c: In function ‘main’: user.c:24:5: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration] int *A = malloc(len * sizeof(int)); ^ user.c:24:14: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] int *A = malloc(len * sizeof(int)); ^ user.c:23:15: warning: unused variable ‘k’ [-Wunused-variable] int i, j, k; ^