Буду по порядку добавлять.

1)

uses crt;
var n,s,i:integer;
begin
clrscr;
write('n=');
readln(n);
s:=0;
for i:=1 to n do
s:=s+sqr(i);
write('s=',s);
end.

2)

uses crt;
var a:array [1..100] of real;
n,i,p,o,l:integer;
begin
clrscr;
write('n=');
readln(n);
write('a[n]:');
for i:=1 to n do
begin
readln(a[n]);
if a[n]>0 then p:=p+1;
if a[n]<0 then o:=o+1;
if a[n]=0 then l:=l+1;
end;
writeln(l,p,o);
end.

3)

uses crt;
var a:array [1..100] of real; i,n:integer;
begin
clrscr;
write('n=');
readln(n);
write('a[n]:');
for i:=1 to n do
read(a[i]);
for i:=1 to n do
if (a[i]=0) then writeln('YES')
else writeln('NO');
end.