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POGetting an overflow error within unchecked statement
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  1. POGetting an overflow error within unchecked statement
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    copied!<pre><code>byte b; int i; unchecked { b = 255 + 255; //overflows i = 100 + int.MaxValue+100; // works } </code></pre> <p>1) Is the reason why b expression (<code>b = 255 + 255;</code>) causes an overflow error due to being affected by two conflicting rules, where first rule <strong>R1</strong> states:</p> <blockquote> <p>A constant-expression (§7.19) of type int can be converted to type sbyte, byte, short, ushort, uint, or ulong, provided the value of the constant-expression is within the range of the destination type.</p> </blockquote> <p>while second rule <strong>R2</strong> states that within unchecked context overflow is allowed. </p> <p>And in the case of b expression, <strong>R1</strong> takes precedence over <strong>R2</strong>, and thus since constant expression <code>255+ 255</code> is not within the range of destination type ( which is byte ), <strong>R1</strong> causes an error, even though <strong>R2</strong> permits an overflow? </p> <p>2) </p> <p>a) Here's my reasoning as to why i expression (<code>i = 100 + int.MaxValue+100;</code>) doesn't cause an error:</p> <p>1 - When compiler starts computing i expression, it doesn't try to promote values <code>100</code> and <code>int.MaxValue</code> to type <code>long</code> before performing the addition ( thus during the computation process the two values are still of type <code>int</code> )</p> <p>2 - the addition does cause an overflow, but since this happens within unchecked context, no error is thrown</p> <p>3 - Since the two values didn't get promoted to <code>long</code>, the resulting value is also of type <code>int</code> and as such the resulting value is within the range of destination type</p> <p>b) But if instead compiler did promote <code>100</code> and <code>int.MaxValue</code>; to type <code>long</code> before performing the addition, then i expression would cause an error due to violation of rule <strong>R1</strong>?!</p> <p>thanx</p>
 

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