C# Comparing 2 strings always return false

Question

I'm trying to make the program respond to certain words sent by a microcontroller, but when I compare the received word with a pre-defined word, it always returns false.

private void ReadData()
{
    if (serialPort1.IsOpen == true)
    {
        if (serialPort1.BytesToRead > 0)
        {
            string readBuffer = serialPort1.ReadLine(); 

            textBox2.Text = readBuffer;
            if (readBuffer.Equals("A")) //MY MAIN PROBLEM
            {
                textBox2.Text += "YEP";
            }
            else
            {
                textBox2.Text += "NOPE";
            }
        }
    }
}

Basically when the microcontroller sends letter "A", it reads it and stores it into the readBuffer string, and even prints it out in a textbox(textBox2). My result is always ANOPE in the textbox (A is what the microcontroller sent and NOPE is always there because the if failed). I started C# recently and lost several days trying to figure this one out, but I really can't seem to find a solution to an apparently simple issue.

Perhaps the new line is included in the readBuffer string? — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jan 9, 2016 at 23:16
Have you debugged this? Maybe there is a \n or some other byte after the A in the string. You did a ReadLine so there may be some new line character that your text box does not display. — René Vogt
– René Vogt, Commented Jan 9, 2016 at 23:18
Thank you for the incredibly fast replies! And yes, it did add a carriage return (\r) after the A, which I couldn't see, but the debbuger caught it! — Danijel Milosevic
– Danijel Milosevic, Commented Jan 9, 2016 at 23:31

Danijel Milosevic · Accepted Answer · 2016-01-09 23:37:48Z

1

Thanks to Willem Van Onsem and René Vogt I figured out the problem. After it reads the data and stores it into the readBuffer, it also includes \r (carriage return), making the string actually "A\r", which is why it was always false compared to "A".

answered Jan 9, 2016 at 23:37

Danijel Milosevic

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1 Comment

Scott Chamberlain Over a year ago

set serialPort1.NewLine = "\r\n" and then ReadLine() will nolonger return the \r

rogerwamba · Accepted Answer · 2016-01-09 23:31:31Z

0

Two things I submit to you:
1. Things are not always as they appear: use readBuffer.Trim().Equals("A") instead.

readBuffer.Equals("A") performs an ordinal (case-sensitive and culture-insensitive) comparison.
A = A but A ≠ a if you use .Equals to compare them.

So in final analysis, try this:
if (readBuffer.Trim().ToUpper().Equals("A"))

answered Jan 9, 2016 at 23:31

rogerwamba

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