Question

What does this code do?

txtCardNo.Text.Trim().Substring((txtCardNo.Text.Trim().Length - 4), 4)

Answer 1

It gets last 4 characters from txtCardNo (without leading or ending spaces) but it would be better if it was like this:

var result = txtCardNo.Text.Trim();
result = result.Substring(result.Length - 4);

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EDIT:

Also, note that this will throw error if trimmed string has less than 4 characters. You could handle it with something like this:

var result = txtCardNo.Text.Trim();
if (result.Length >=4)
   result = result.Substring(result.Length - 4);
else
   // do domething