Integer summing blues, short += short problem

by

There are two questions here. The first is “why is short plus short result in int?”

Well, suppose short plus short was short and see what happens:

short[] prices = { 10000, 15000, 11000 };
short average = (prices[0] + prices[1] + prices[2]) / 3;

And the average is, of course, -9845 if this calculation is done in shorts. The sum is larger than the largest possible short, so it wraps around to negative, and then you divide the negative number.

In a world where integer arithmetic wraps around it is much more sensible to do all the calculations in int, a type which is likely to have enough range for typical calculations to not overflow.

The second question is:

  • short plus short is int
  • assigning int to short is illegal
  • a +=b is the same as a = a + b
  • therefore short += short should be illegal
  • so why is this legal?

The question has an incorrect premise; the third line above is wrong. The C# specification states in section 7.17.2

Otherwise, if the selected operator is
a predefined operator, if the return
type of the selected operator is
explicitly convertible to the type of
x, and if y is implicitly convertible
to the type of x or the operator is a
shift operator, then the operation is
evaluated as x = (T)(x op y), where T
is the type of x, except that x is
evaluated only once.

The compiler inserts the cast on your behalf. The correct reasoning is:

  • short plus short is int
  • assigning int to short is illegal
  • s1 += s2 is the same as s1 = (short)(s1 + s2)
  • therefore this should be legal

If it did not insert the cast for you then it would be impossible to use compound assignment on many types.

More Related Contents:

  1. c# home works can’t solve [closed]
  2. Input string not in a correct format [closed]
  3. Get int value from enum in C#
  4. How can I convert String to Int?
  5. How to create a new object instance from a Type
  6. Quickest way to convert a base 10 number to any base in .NET?
  7. String was not recognized as a valid DateTime ” format dd/MM/yyyy”
  8. How To Change DataType of a DataColumn in a DataTable?
  9. Generics in C#, using type of a variable as parameter [duplicate]
  10. Casting a variable using a Type variable
  11. C# use System.Type as Generic parameter
  12. Why should I use int instead of a byte or short in C#
  13. Using IsAssignableFrom with ‘open’ generic types
  14. How can I get the data type of a variable in C#?
  15. .NET : How do you get the Type of a null object?
  16. Determine if a type is static
  17. Finding the Concrete Type behind an Interface instance
  18. What are the differences between value types and reference types in C#? [duplicate]
  19. Performing Math operations on decimal datatype in C#?
  20. How to get the most common value in an Int array? (C#)
  21. How to switch between “possible” type of an object? [duplicate]
  22. What to do when bit mask (flags) enum gets too large
  23. dynamic vs object type
  24. C#: Oracle Data Type Equivalence with OracleDbType
  25. What’s the difference between ‘int?’ and ‘int’ in C#?
  26. PostgreSQL and C# Datatypes
  27. Int to string: cannot convert from ‘method group’ to ‘string’ [closed]
  28. C# dynamic type gotcha
  29. How do I convert a decimal to an int in C#?
  30. What is the “base class” for numeric value types?

Leave a Comment