How can I resolve the System.FormatException error that states that the index (beginning at zero) needs to be a value that is greater than or equal to zero, and less than the size of the argument list?

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This error occurs when attempting to format a string with an invalid index value. To resolve this error, check the index value being passed in the format string to ensure that it is valid and within the bounds of the argument list.

Ensure that you have the correct number of index placeholders in the format string and that the corresponding values in the argument list match the index position. Also, ensure that any variable values you are trying to insert into the string are properly formatted and have the correct data type.

If you are using a variable or expression for the index value, ensure that it is evaluated correctly and returns a valid index value.

Additionally, you can use string interpolation or composite formatting instead of using string.Format to ensure that the values are properly matched and formatted.

Example of composite formatting:

string name = "John"; int age = 30; Console.WriteLine("My name is {0} and I am {1} years old.", name, age);

Example of string interpolation:

string name = "John"; int age = 30; Console.WriteLine($"My name is {name} and I am {age} years old.");