1.)

var c: array [1..100] of string;

3.)

var u: array [1..20] of integer;
i: integer;
begin
for i:=1 to 20 do
begin
write('u[', i, '] = ');
readln(u[i]);
end;
end.

4.)

var y: array [1..11] of real;
i: integer;
begin
for i:=-1 to 9 do
u[i+2]:=3/(i+2);
writeln(u[6]);
writeln(u[10]);
end.

5.)

h[2]:=h[2]*3;
h[1]:=sqr(h[5]);