Multiply numbers between textboxes

Question

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When I remove number from textBox5, the code errors out;
int R = Convert.ToInt32(textBox4.Text);
//int I = Convert.ToInt32(textBox5.Text);

//int E = R * I;

//textBox6.Text = E.ToString();

The second way I tried is below: Both codes error out when I remove number and try to put in a new number.

int R = int.Parse(textBox4.Text);
int I = int.Parse(textBox5.Text);

int E = R * I;

textBox6.Text = E.ToString();

What I have tried:

The two ways in the description

Posted 30-Nov-17 2:41am

Member 12457690

Updated 30-Nov-17 3:10am

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Comments

Richard MacCutchan 30-Nov-17 8:56am

What sort of error?Please give proper details of the problem.

2 solutions

Solution 2

When you remove the number from the textbox, then an empty string is passed to the ToInt32 method, which raises the error because it cannot convert an empty string to a integer value.
Int32.Parse method does as well.
You have several options:
- allow input of empty strings in the TextBox and interpret empty strings as a default value of zero.
- handle the Validating event of the TextBox and do not allow to loose focus until there is an integer value in there (not very user friendly).
- have an error provider spotting the missing value.

There is one rule that is never blindly trust user inputs, always assume there will be input errors, so code to handle all test cases. The TryParse method could be a good choice to test for input values. A better option than the Convert class which is not a very good tool for the task at hand, anyway.

Hope this helps.

Posted 30-Nov-17 3:09am

phil.o

Updated 30-Nov-17 3:10am

v2

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F-ES Sitecore · Accepted Answer · 2017-11-30T02:59:00

Convert.ToInt32 and int.Parse are only suitable if you know the text can be converted to an int, as you are working with user input you don't know if it is valid, so use int.TryParse instead.

int R = 0;
int I = 0;

if (!int.TryParse(textBox4.Text.Trim(), out R))
{
    // if the code gets here the conversion to int failed
    // you can show a message to the user, or give R a default value
    // do whatever your code requires

    R = 0;
}

if (!int.TryParse(textBox5.Text.Trim(), out I))
{
    // if the code gets here the conversion to int failed
    // you can show a message to the user, or give I a default value
    // do whatever your code requires

    I = 0;
}

int E = R * I;