Compilare: user.c: In function ‘factorial’: user.c:20:9: warning: implicit declaration of function ‘multiply’ [-Wimplicit-function-declaration] res_size = multiply(x, res, res_size); ^ user.c: In function ‘main’: user.c:55:17: warning: unused variable ‘i’ [-Wunused-variable] int N, factN=1, i; ^ user.c:55:8: warning: unused variable ‘factN’ [-Wunused-variable] int N, factN=1, i; ^ user.c:60:7: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(file1, "%d", &N); ^