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

Answer 1

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?