C :

#include <stdio.h>
#include <stdlib.h>
int main()
{
	int y,m,a[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
    scanf("%d%d",&y,&m);
    if(m!=2)
        printf("%d",a[m]);
    if(m==2)
        if(y%4==0 || y%400==0)
            printf("29");
        else
            printf("28");
	return 0;
}

C++ :

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    int year,month;
    cin>>year>>month;
    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;
    }
    return 0;
}

Pascal :

program xx;
var year,month,days:integer;
begin
read(year,month);
case month of
    1,3,5,7,8,10,12: days:=31;
    4,6,9,11       : days:=30;
    2              : if (year mod 4=0)and(year mod 100 <>0)
                        or(year mod 400=0)
                        then days:=29
                        else days:=28
end;
writeln(days);
end.