{“输入字符串的格式不正确。”}

Question

I cannot figure out wh i am getting error

"{"Input string was not in a correct format."}"

When I type for example 5+5 into my Sum Textbox and click equals which should then display my answer in my answer textbox, however when I type 5+5 I get the error show above and I cant seem to fix it.

Here is my addition button code

    private void Addition_Click(object sender, EventArgs e)
    {
        dbl_FirstNumber = Convert.ToDouble(Sum.Text); //Operation Works, need to get rid of the 0
        Sum.AppendText(" + ");

Here is my equal button code

    private void equals_Click(object sender, EventArgs e)
    {
        string[] hold = Sum.Text.Split(' ');//
        switch (hold[1])//holds the first number

        {
            case "+":
                Result.Text = Convert.ToString(Convert.ToDouble(Sum.Text) + hold[0].ToString() + hold[2].ToString());   
                break;   

My second problem

Ok so when i try put in 3 + 3 + 3 i get the error "{"Input string was not in a correct format."}"

here is my addition code

     private void Addition_Click(object sender, EventArgs e)
    {
        dbl_FirstNumber = Convert.ToDouble(Sum.Text); 
        Sum.AppendText(" + ");

    }

screenshot of error - https://gyazo.com/9689d4f5055d7cc9211e1c2822b1d6f3

Answer 1

There are mistakes ...

private void equals_Click(object sender, EventArgs e)
{
    string[] hold = Sum.Text.Split(' ');
    switch (hold[1]) // holds the DELIMTER
    {
        case "+":
            Result.Text = Convert.ToString(Convert.ToDouble(Sum.Text) + hold[0].ToString() + hold[2].ToString());   
            // THATS WRONG!                                 ^ this would take "5 + 5" and you CANNOT convert this.
            // here you would Need: 
            Result.Text = (Convert.ToDouble(hold[0]) + Convert.ToDouble(hold[2])).ToString();

            break;