C++ :

#include<iostream>
using namespace std;
int main()
{
	int n;
	cin>>n;
	for (int i=1; i<=n; i++)
	{
		for (int j=1; j<=n; j++) cout<<"#";
		cout<<endl;
	}
	return 0;
}

Pascal :

var n,i,j:longint;
begin
  readln(n);
  for i:=1 to n do
      begin
        for j:=1 to n do write('#');
        writeln;
      end;
end.