Result shows asterisk when converting int to varchar

I was sent a code by one engineer saying they he gets an odd error with one of calculations written. He gets the following error;

Conversion failed when converting the varchar value '* ' to data type int.

By looking at the error, I realized the issue, it is related to truncation. He converts a numeric value to a varchar variable and then again he uses the converted varchar value with another calculation, converting to back to int. This calculation causes the error because previously converted value contains asterisk, not the numeric value that was used with initial conversion.

How can it be happened? This happens when you convert character or binary expressions to an expression of a different data type. If the the result cannot be accommadate with the set data type, SQL Server either truncates the value, partially displays or throw an error.

See this code;

DECLARE @x int = 1000;
DECLARE @y char(2);

SET @y = @x;
SELECT @y;

When the value 1000 is converted to char(2), the result becomes asterisk because the set data type cannot hold 1000. The asterisk indicates that value is truncated.

Here are some known results when converting to an expression of a different data type.