How to get a number from a textbox

Question

I have 3 text boxes, and I want the user to put any number into it to get an answer.

Here is the code I have so far:

int firstNumber;
int secondNumber;
int thirdNumber;
int answer;
firstNumber = 100;
secondNumber = 75;
thirdNumber = 50;
answer = firstNumber + secondNumber * thirdNumber;
MessageBox.Show(answer.ToString());

Answer 1

To convert a string to int, use Int32.Parse or Int32.TryParse or Convert.ToInt32

int firstNumber = Int32.Parse(firstNumberTextBox.Text);
//throws exception if not convertible

or

int firstNumber;
bool result = Int32.TryParse(firstNumberTextBox.Text, out firstNumber);
//return false if not convertible

or

int firstNumber;
result = Convert.ToInt32(firstNumberTextBox.Text);
//throws exception if not convertible

Using the Convert.ToInt32(String) method is equivalent to passing value to the Int32.Parse(String) method. value is interpreted by using the formatting conventions of the current thread culture.

If you prefer not to handle an exception if the conversion fails, you can call the Int32.TryParse method instead. It returns a Boolean value that indicates whether the conversion succeeded or failed.

You can use int instead of Int32.

So in your case, it seems int.TryPars better fits:

int firstNumber;
int secondNumber;
int thirdNumber;
int answer;
int.TryParse(firstNumberTextBox.Text, out firstNumber);
int.TryParse(secondNumberTextBox.Text, out secondNumber);
int.TryParse(thirdNumberTextBox.Text, out thirdNumber);
answer = firstNumber + secondNumber * thirdNumber;
MessageBox.Show(answer.ToString());

Answer 2

Here how to use Convert.ToInt32() method,

int firstNumber;
int secondNumber;
int thirdNumber;
int answer;
firstNumber = Convert.ToInt32(textBox1.Text);
secondNumber = Convert.ToInt32(textBox2.Text);
thirdNumber = Convert.ToInt32(textBox2.Text);
answer = firstNumber + secondNumber* thirdNumber;
MessageBox.Show(answer.ToString());

but the problem in here is when the value of textbox is not convertible to integer your application will give an error.

Answer 3

As pointed out already Int32.TryParse will protect you from an exception if the user types in a value that's not a number.

But I would advise to prevent the user from typing in invalid values. You can achieve that by handling the KeyPress event

private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) &&
        (e.KeyChar != '.'))
    {
        e.Handled = true;
    }

    // only allow one decimal point
    if ((e.KeyChar == '.') && ((sender as TextBox).Text.IndexOf('.') > -1))
    {
        e.Handled = true;
    }
}

Check this post for more details.

This way you will make sure the input is valid and it's safe to use Int32.Parse or Convert.ToInt32.

Answer 4

Create a Form or Window where you have 3 TextBoxes naming firstNumber, secondNumber, thirdNumber and than the calculations could be done something like this

MessageBox.Show((Convert.ToInt32(firstNumber.Text) +
                 Convert.ToInt32(secondNumber.Text) *
                 Convert.ToInt32(thirdNumber.Text)).ToString());

Less code to do the same thing (and possibly better).

Answer 5

1. Create a Form or Window where you have 3 TextBoxes naming firstNumber, secondNumber, thirdNumber.
2. Test for digits:

private void TxtBox1_KeyPress(object sender, KeyPressEventArgs e)
    {
         if (!Char.IsDigit(e.KeyChar))
              e.Handled = true;
    }
 //To allow for backspace:
    private void TxtBox1_KeyPress(object sender, KeyPressEventArgs e)
    {
         if (!(Char.IsDigit(e.KeyChar) && (e.KeyChar == (char)Keys.Back)))
              e.Handled = true;
    }

If you want to add other allowable keys, look at the Keys enumeration and use the approach above. 3. To convert a string to int, use Int32.Parse.
4. Add & display the answer.