擅长:python、mysql、java
<p>这是<a href="http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html" rel="nofollow">round-off error</a>的一个例子:</p>
<blockquote>
<p><em>Squeezing infinitely many real numbers into a finite number of bits requires an approximate representation. Although there are infinitely many integers, in most programs the result of integer computations can be stored in 32 bits. In contrast, given any fixed number of bits, most calculations with real numbers will produce quantities that cannot be exactly represented using that many bits. Therefore the result of a floating-point calculation must often be rounded in order to fit back into its finite representation. This rounding error is the characteristic feature of floating-point computation.</em></p>
</blockquote>
<p>通过执行以下操作,您将离您想要的位置足够近:</p>
<pre><code>def sumof3(n):
n = float((n-1)/3)
return int((n/2)*(6+3*(n-1)))
</code></pre>
<p>或者如果你想说得更准确些:</p>
<pre><code>def sumof3(n):
n = float((n-1)/3)
return float((n/2)*(6+3*(n-1)))
</code></pre>