Checking multiple conditions for a string in C#

Question

I want to check multiple conditions in a string in C# but it throws error saying Cannot use && for string or boolean

if ((duStart.Trim() != "" && duStart.Trim() != null) &&(duEnd.Trim() != "" && duEnd.Trim() != null))
{
//do this
}
else
//do that

Trim() cannot return null. Look at the String.IsNullOrWhiteSpace() method. — SLaks
– SLaks, Commented Jan 10, 2011 at 20:12
The code you have posted compiles. The error is somewhere else. Please post the relevant part of your code. — Darin Dimitrov
– Darin Dimitrov, Commented Jan 10, 2011 at 20:13

Jon Skeet · Accepted Answer · 2011-01-10 20:12:35Z

2

The code you've given compiles fine. Here's a short but complete program - I've changed the whitespace of your line of code, but that's all:

using System;

class Test
{
    static void Main()
    {
        string duStart = "X";
        string duEnd = "X";
        if ((duStart.Trim() != "" && duStart.Trim() != null) &&
            (duEnd.Trim() != "" && duEnd.Trim() != null))
        {
            Console.WriteLine("Yes");
        }
    }
}

Having said that:

If you're going to use the same value (the trimmed version of duStart, for example) multiple times, there seems little point in computing it twice. I'd have used extra local variables (trimmedStart, trimmedEnd) here
Trim never returns null, so those tests are pointless.
Using string.IsNullOrWhitespace is probably a better idea here. Why bother creating strings that you're never going to use?

answered Jan 10, 2011 at 20:12

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Felice Pollano Over a year ago

Btw the strange null check could mean that the originals duStart and duEnd could be null, if this is the case a check has to be done before

Jon Skeet Over a year ago

@Felice: Nope, because then calling duStart.Trim() would throw an exception to start with, wouldn't it?

Felice Pollano · Accepted Answer · 2011-01-10 20:14:22Z

1

you can simplify the condition by writing:

if( !string.IsNullOrEmpty(duStart.Trim()) && !string.isNullOrEmpty(duEnd.Trim()) )
{
}

answered Jan 10, 2011 at 20:14

Felice Pollano

33.4k10 gold badges77 silver badges125 bronze badges

1 Comment

Felice Pollano Over a year ago

Better to use the suggestion of SLaks, IsNullOrWhiteSpace, and avoid using Trim at all.

HariM · Accepted Answer · 2011-01-10 20:27:23Z

0

Check for the Null first for duStart and duEnd. Then try Trim the string. Trim cannot be applied on a null value. So, below code block should work for you.

if ((duStart != null && duStart.Trim() != "") && (duEnd != null && duEnd.Trim() != ""))
{ 
   //do this 
}
else
{
   //do that 
}

answered Jan 10, 2011 at 20:27

HariM

11 bronze badge

Collectives™ on Stack Overflow

Checking multiple conditions for a string in C#

3 Answers 3

2 Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related