Why Does `short = short` Work in C# While `short = short short` Doesn't?

Integer overflow and arithmetic assignment operators in C#: short = short

In C#, when two short integers are added, the result will be a int type with a larger range of values ​​than short. Integer overflow occurs if the sum of two short integers exceeds the maximum value of short.

Consider the following code:

<code class="language-csharp">short a, b;
a = 10;
b = 10;
a = a + b; // 错误：无法隐式转换类型“int”为“short”。</code>

Here, the addition operation result of a and b is of type int, and the compiler cannot implicitly convert it to type short. This is because assigning int to short without an explicit conversion results in data loss.

However, the following code does not produce an error:

<code class="language-csharp">a += b; // 但这段代码可以成功运行，为什么？</code>

This is because C# handles the arithmetic assignment operator = differently. When using =, the compiler internally does the following:

<code class="language-csharp">a = (short)(a + b);</code>

The compiler will automatically convert the result of the addition operation to the a type before assigning the result to short. This ensures that the value is correctly stored in the int variable even if the intermediate result is of type short.

This behavior is similar to other compound assignment operators, such as -=, *=, and /=, which automatically convert the result to the type of the left operand.

Thus, the arithmetic assignment operator short can be safely used on = variables even if the sum exceeds the range of short. The compiler handles type conversion internally to avoid integer overflow errors.

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