foo.cc:18:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
 main(){
      ^
foo.cc: In function 'int main()':
foo.cc:23:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&i,&j);
  ~~~~~^~~~~~~~~~~~~~~
foo.cc:24:23: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(k=0;k<i;k++)scanf("%d",&a[k]);
                  ~~~~~^~~~~~~~~~~~
foo.cc:25:23: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(k=0;k<j;k++)scanf("%d",&b[k]);
                  ~~~~~^~~~~~~~~~~~

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