Question

private void button2_Click(object sender, EventArgs e)
{
    int i = 5;
    MessageBox.Show(i);
}

Fails..

private void button2_Click(object sender, EventArgs e)
{
    int i = 5;
    MessageBox.Show("hoo" + i);
}

Works. Why is that??

Answer 1

MessageBox.Show() requires a string as its input parameter.

The first sample fails because there is no implicit conversion from integer to string.

The second sample succeeds because "hoo" + i evaluates to a string. This happens because the C# language defines an addition operator which accepts a string and an object. The object is converted to a string by calling ToString(). This string addition operator is always selected when one of the operands to the addition is a string.