Main.cc:39:9: error: ‘::main’ must return ‘int’ ll main(){ ^ Main.cc: In function ‘int main()’: Main.cc:42:7: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%lld",&n); ~~~~~^~~~~~~~~~~ Main.cc:45:8: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%lld",&a[i]); ~~~~~^~~~~~~~~~~~~~