C＃如何将“ ||”与“！=”组合使用？

Question

Why does adding an "||" OR between 2 "!=" not work for me?

When 'name' is "test" or "test2" my if statement doesn't work if I've used 2 "!=" but if I use just one it does, please tell me why.

if (col.Name != "test" || col.Name != "test2")
 {
  MessageBox.Show("No" + col.Name.ToString()); //This shows "No test" and "No test2"
 }
  else
 {
  MessageBox.Show("YES " + col.Name.ToString()); //does not reach here
 }

this works with no "||".

if (col.Name != "test")
 {
  MessageBox.Show("No" + col.Name.ToString());
 }
  else
 {
  MessageBox.Show("YES " + col.Name.ToString()); //Shows "YES test"
 }

Thanks all

Answer 1

try this:

col.Name != "test" && col.Name != "test2"

think about it... "if the number is not 1, or the number is not 2" will always be true, since no number is both 1 and 2 to makes both halves false. Now extend this to strings.

Answer 2

It works, but it's not what you want.

col.Name != "test" || col.Name != "test2"

always returns true , since if col.Name is "test", it's not "test2", so you have "false || true" => true. If col.Name is "test2", you get "true || false". If it's anything else, it evaluates to "true || true".

I can't be sure exactly what you want to do, but you probably need an and ( && ) between them.

Answer 3

You need to do a AND and not a OR :)

Pseudo code:

if string1 not equal test AND not equal test2 than do...

Here is the version corrected :

if (col.Name != "test" && col.Name != "test2")
{
  MessageBox.Show("No" + col.Name.ToString()); //This shows "No test" and "No test2"
}
else
{
  MessageBox.Show("YES " + col.Name.ToString()); //does not reach here
}

Answer 4

You're using OR, consider the truth table:

p          q        p || q
true      true      true
true      false     true
false     true      true
false     false     false

You should use AND for the desired behavior...