Question

The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.

Find the sum of all the primes below two million.

And my answer is:

bool IsRishoni;
int soap = 0;
for (int i = 3; i < 2000000; i++)
{
    IsRishoni = true;
    for (int a = 2; (a <= Math.Sqrt(i)) && (IsRishoni); a++)
    {
        if (i % a == 0)
            IsRishoni = false;
    }
    if (IsRishoni)
    {
        soap = i + soap;
    }
}
Console.WriteLine(soap + 2);
Console.ReadLine();

Why is this not working? the answer I got is 1179908154 … help please.

Answer 1

Replace

soap = i + soap;

with

soap = checked(i + soap);

..and the problem should be exposed.

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