foo.cc: In function 'int main()':
foo.cc:6:27: warning: unused variable 'j' [-Wunused-variable]
     int i,ans=0,sum=0,num,j,k=0;
                           ^
foo.cc:6:29: warning: unused variable 'k' [-Wunused-variable]
     int i,ans=0,sum=0,num,j,k=0;
                             ^
foo.cc:7:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &N);
     ~~~~~^~~~~~~~~~
foo.cc:8:28: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for(i=0;i<N;i++) {scanf("%d",&A[i]);sum+=A[i];}
                       ~~~~~^~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。