Question

I’m doing the problems on Project Euler in C++, but I’m not getting the right answers to the first one.

Here’s my code:

#include <iostream>

using namespace std;

int main()
{
    int b;
    int c;

    for (int a = 0; a <= 1000;)
    {
        a = a + 3;
        b = a + b;
    }
    cout << b << "\n";

    for (int a = 0; a <=1000;)
    {
        a = a + 5;
        c = a + c;
    }
    cout << c << "\n";

    b = b + c;
    cout << b << "\n";
    return 0;
}

My output is:

167835
101505
269340

Where’s the error in my logic?

Answer 1

You are adding all values that are both multiples of 3 and 5 (i.e. multiples of 15) twice. Additionally, you will also include 1002 and 1005, which probably isn’t intended.