C++ :

#include <cstdio>
int main(void) {
	int y0, m0, d0, y, m, d, s=0, i;
	int md[12]={31,28,31,30,31,30,31,31,30,31,30,31};
	scanf("%d%d%d%d%d%d", &y0, &m0, &d0, &y, &m, &d);
	y0 += 19; //目标年份
	if(y%400==0 || y%4==0&&y%100>0) md[1] = 29;
	for(s=-d, i=0; i<m-1; ++i) s -= md[i]; // 负数表示当年已过的天数
	for(; y<y0; ++y) { //中间年份的天数
		if(y%400==0 || y%4==0&&y%100>0) s += 366;
		else s += 365;
	}
	if(y%400==0 || y%4==0&&y%100>0) md[1] = 29;
	else  md[1] = 28;
	for(i=0, s+=d0; i<m0-1; ++i) s += md[i];
	printf("%d\n", s);
	return 0;
}

Pascal :

Var
month:array[1..12]of longint;
ans,yy,mm,dd,y,m,d:longint;
function check(x:longint):boolean;
begin
        if (x mod 400=0)or(x mod 100<>0)and(x mod 4=0) then exit(true);
        exit(false);
end;
begin
{assign(input,'days.in');reset(input);
assign(output,'days.out');rewrite(output);}
        ans:=0;
        month[1]:=31;month[2]:=28;month[3]:=31;
        month[4]:=30;month[5]:=31;month[6]:=30;
        month[7]:=31;month[8]:=31;month[9]:=30;
        month[10]:=31;month[11]:=30;month[12]:=31;
        read(yy,mm,dd);
        read(y,m,d);
        yy:=yy+19;
        while (y<>yy)or(m<>mm)or(d<>dd) do
        begin
                inc(ans);
                if check(y) then month[2]:=29 else
                month[2]:=28;
                inc(d);
                if d>month[m] then
                begin
                        inc(m);
                        d:=1;
                end;
                if m>12 then
                begin
                        m:=1;
                        inc(y);
                end;
        end;
        writeln(ans);
{close(input);
close(output);}
end.