if (x != 1-9999999) {}

[aewarnick]

if (x != 1-9999999) {}

 

How would I write that?

[Volte]

if ((x < 1) || (x > 9999999)) 
{
MessageBox.Show("x is not between 1 and 9999999");
}

[aewarnick]

I said that wrong. Here is what I am really trying to do. I have a text box called x and I have a picture that the user clicks on to calculate something but if they enter in anything out of range or a character the program fails. How do I prevent it?

 

if ((float.Parse(x.Text) >- 1)||(float.Parse(x.Text) < 9999999))

 

The probelm with that is if the user enters in a character it cannot convert it safely. How do I check to see if what was entered was a character or number?

Edited February 1, 2003 by aewarnick

[Volte]

Put the following function in your code:

private bool isNum(string str) 
{
try   { int dummy = int.Parse(str); }
catch { return false; }
return true;
}

And then you can use

if (isNum(x.Text))
{
 int num = int.Parse(x.Text);
 if ((num < -1)||(num > 9999999))
 {
   // it's valid
 }
}

[aewarnick]

That works perfectly!

 

How does if know to execute the loop if true or false is returned without putting:

 

if (isNum(x.Text)==true)

[Volte]

Ah, booleans can be pretty confusing for someone new to programming.

 

If statements operate solely on booleans; the block of code in the "if"

is only executed if the condition in the "if" statement is true.

The condition in the "if" is always a boolean. For

example, in the code

if (x == 6)

"x == 6" is a boolean. When you use a comparison operator in an

expression, the expression will be evaluated and return true

or false based on, obviously, whether the expression is true

or false.

 

So basically, if (x == 6) is evaluated as if (true) is x does indeed

equal 6, or if (false) otherwise. When evaluating a boolean

variable, it automatically returns true or false without needing

a comparison operator.

Essentially,

if (someBool == true)

is evaluated as

if ((someBool == true) == true)

and that's not really very efficient.

 

[edit]Oooops... I meant "x == 6". not "x = 6"[/edit]

Edited February 1, 2003 by Volte

[aewarnick]

Very, Very good explanation. Thank you!!

[Volte]

You're welcome. :)

 

One other thing I forgot to mention is that if you want to

only execute code if a boolean is false, then you would

do this:

if (!someBool)
{
 //someBool is false
}

[aewarnick]

What if I come accross a situation where I can only test to see if a user enters in characters or numbers but I cannot test by using try/catch.

 

if (textbox1==(char)){}???

if (textbox1==(int)){}???

if (textbox1==(double)){}???

[Volte]

Well, there is another way you can do it with looping through every

character. For example:

private bool isNum(string str) 
{
char[] chr = str.ToCharArray();
		
foreach (char dummy in chr)
  if (!char.IsDigit(dummy)) return false;
         
return true;
}

Is another way to check to see if it's numeric, while

private bool isChar(string str) 
{
char[] chr = str.ToCharArray();
		
foreach (char dummy in chr)
  if (!char.IsLetter(dummy)) return false;
         
return true;
}

is a way to test to see if it's letters only. Just change the 'IsLetter'

function to one of the other checks (they are listed in MSDN and the

intellisense).

[aewarnick]

I'll try it out later. I am gathering all this info so that I don't forget it. Thank you.