How to Build .NET Strings at Run Time
You want to put together an error message that includes information from the Customer object that caused the problem. Since you're not repeatedly modifying a single string variable, using StringBuilder would be overkill. You still have three options.
Your first option is the most obvious: Concatenation. Here's some code that assembles a message from constant string and some values:
string msg = "Customer " + cust.Id + " has an invalid status " + cust.Status;
Your second option is to use the string class's Format method. You're probably used to seeing this syntax because there are lots of functions that use string.Format under the hood to build strings. With the Format method, you provide your constant string as your first parameter. Inside that string you put place holders (marked with curly braces: { }) where the variable data is to be inserted. The Format method will insert the values from the following parameters into the place holders.
Here's my message with the Format method:
string msg = string.Format("Customer {0} has an invalid status {1}.", cust.Id, cust.Status);
Your third option is string interpolation. This is the newest mechanism and is what all the "hip and happening" developers use. It looks much like using the Format method, but the placeholders now hold the values to be inserted into the string. You need to flag the string with a dollar sign ($) to tell C# that the curly braces are to be treated as placeholders rather than included in the string:
string msg = $"Customer {cust.Id} has an invalid status {cust.Status}.";
Posted by Peter Vogel on 05/29/2019