Logical operator || in C# does not work

Question

I’m trying to do an exercise where in a range of 0 to 30 I want to know which numbers are divisible by 3 or 4. Working with a if for every situation works. But if I try to use the logical operator || does not work. It is part of the code that is commented.

private void button5_Click(object sender, EventArgs e)
{
    int iA;

    for (iA = 0; iA <= 30; iA++)
    {
        //if (iA % 3 == 0 || iA % 4 == 0);
        //{
        //    MessageBox.Show(iA + " é múltiplo de 3 ou de 4");
        //}
        if (iA % 3 == 0)
        {
            MessageBox.Show(iA + " é múltiplo de 3");
        }
        else if (iA % 4 == 0)
        {
            MessageBox.Show(iA + " é múltiplo de 4");
        }

    }
}

Answer 1

The problem is that you’re putting one ; in the if and is closing it. The right thing would be:

using static System.Console;

public class Program {
    public static void Main() {
        for (var iA = 0; iA <= 30; iA++) if (iA % 3 == 0 || iA % 4 == 0) WriteLine(iA + " é múltiplo de 3 ou de 4");
    }
}

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference.

Answer 2

Your instruction if is being shut down on the first line, as it has a ; with that, the two MessageBox are called sequentially.

---

A palliative solution to this scenario is with the use of Linq:
Obs: If the intention is to display a message to the user at each occurrence, then disregard.

var listaNumeros = Enumerable.Range(1, 30).Where(p => p % 3 ==0 || p % 4 == 0).ToList();

With the Linq you can:

• Create a list of how many sequential numbers you want;
• Filter directly into this list according to your conditions;

Answer 3

I found the error. The if structure does not end with ";". Thankful