C++ :

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    int year,month;
    while(scanf("%d%d",&year,&month)==2)
    {
        switch (month)
        {
            case 1:
            case 3:
            case 5:
            case 7:
            case 8:
            case 10:
            case 12:
                cout<<31<<endl;
                break;
            case 4:
            case 6:
            case 9:
            case 11:
                cout<<30<<endl;
                break;
            default:
                //2月
                if( (year%100 != 0  && year%4 == 0) || (year%400 == 0) )
                {
                    //如果是闰年，2月29天
                    cout<<29<<endl;
                }
                else
                {
                    //如果是平年，2月28天
                    cout<<28<<endl;
                }
                break;
        }
    }
}

Pascal :

var
  x,y,d:longint;
  leap:boolean;
begin
  while not eof do 
  begin
  readln(x,y);
  if ((x mod 4=0)and(x mod 100<>0))or(x mod 400=0)then
    leap:=true
  else
    leap:=false;
  case y of
  1,3,5,7,8,10,12:d:=31;
  4,6,9,11:d:=30;
  2:if leap then d:=29
    else d:=28;
  end;
  writeln(d);
  end;

  readln;
end.