Pascal - How do i sum all the numbers that can be divided by 4, must use repeat

Question

Cant obtain a correct answer it sums incorectly and multiplicates too, i must use repeat when solving this problem, i suppose the problem is in sum:=i+i but i dont know how to solve it

program SAD;
uses crt;
var a, i, sum, prod: integer;
begin
clrscr;
sum:=0;
prod:=0;
{Sum}
repeat
for i:=1 to 26 do
if i mod 4 = 0 then sum:=i+i;
until i = 26;
{Multiplication}
repeat
for a:=1 to 26 do
if a mod 4 = 0 then prod:=a*a;
until a = 26;
writeln('Suma numerelor divizate la 4 este:', sum);
writeln('Produsul numerelor divizate la 4 este:', prod);
end.

Answer 1

I think the instruction "use repeat" probably intends that you should avoid using for as well.

There are a few errors in your code:

1. In the sum loop, you should add i to sum, not to itself.

2. In the prod loop, since you set prod to zero at the start, it will stay as zero because zero times anything is zero. So you need to adjust the logic of your prod calculation so that if prod is zero, when the mod 4 condition is satisfied, you set prod to the current value of a, otherwise you multiply it by a.

Here is some code which fixes the above points and avoids the use of for.

program Sad;
uses crt;
var
  a, i, sum, prod: integer;
begin
  clrscr;
  sum:=0;
  prod:=0;

  {Sum}
  i := 0;
  repeat
    inc(i);
    if (i mod 4) = 0 then
      sum := sum + i;
  until i = 26;

  {Multiplication}
  a :=0;
  repeat
    inc(a);
    if a mod 4 = 0 then begin
      if prod = 0 then
        prod := a
      else
        prod := prod * a;
    end;
  until a = 26;
  writeln('Suma numerelor divizate la 4 este:', sum);
  writeln('Produsul numerelor divizate la 4 este:', prod);
  readln;
end.