PAT/source/html/b1054.html

求平均值
<div class="ques-view"><p>本题的基本要求非常简单：给定 <span class="katex"><span class="katex-mathml"><math><mrow><mi>N</mi></mrow>N</math></span><span aria-hidden="true" class="katex-html"><span class="strut" style="height:0.68333em;"></span><span class="strut bottom" style="height:0.68333em;vertical-align:0em;"></span><span class="base textstyle uncramped"><span class="mord mathit" style="margin-right:0.10903em;">N</span></span></span></span> 个实数，计算它们的平均值。但复杂的是有些输入数据可能是非法的。一个“合法”的输入是 [<span class="katex"><span class="katex-mathml"><math><mrow><mo>−</mo><mn>1</mn><mn>0</mn><mn>0</mn><mn>0</mn><mo separator="true">,</mo><mn>1</mn><mn>0</mn><mn>0</mn><mn>0</mn></mrow>-1000, 1000</math></span><span aria-hidden="true" class="katex-html"><span class="strut" style="height:0.64444em;"></span><span class="strut bottom" style="height:0.8388800000000001em;vertical-align:-0.19444em;"></span><span class="base textstyle uncramped"><span class="mord">−</span><span class="mord mathrm">1</span><span class="mord mathrm">0</span><span class="mord mathrm">0</span><span class="mord mathrm">0</span><span class="mpunct">,</span><span class="mord mathrm">1</span><span class="mord mathrm">0</span><span class="mord mathrm">0</span><span class="mord mathrm">0</span></span></span></span>] 区间内的实数，并且最多精确到小数点后 2 位。当你计算平均值的时候，不能把那些非法的数据算在内。</p>
<h3 id="-">输入格式：</h3>
<p>输入第一行给出正整数 <span class="katex"><span class="katex-mathml"><math><mrow><mi>N</mi></mrow>N</math></span><span aria-hidden="true" class="katex-html"><span class="strut" style="height:0.68333em;"></span><span class="strut bottom" style="height:0.68333em;vertical-align:0em;"></span><span class="base textstyle uncramped"><span class="mord mathit" style="margin-right:0.10903em;">N</span></span></span></span>（<span class="katex"><span class="katex-mathml"><math><mrow><mo>≤</mo><mn>1</mn><mn>0</mn><mn>0</mn></mrow>\le 100</math></span><span aria-hidden="true" class="katex-html"><span class="strut" style="height:0.64444em;"></span><span class="strut bottom" style="height:0.78041em;vertical-align:-0.13597em;"></span><span class="base textstyle uncramped"><span class="mrel">≤</span><span class="mord mathrm">1</span><span class="mord mathrm">0</span><span class="mord mathrm">0</span></span></span></span>）。随后一行给出 <span class="katex"><span class="katex-mathml"><math><mrow><mi>N</mi></mrow>N</math></span><span aria-hidden="true" class="katex-html"><span class="strut" style="height:0.68333em;"></span><span class="strut bottom" style="height:0.68333em;vertical-align:0em;"></span><span class="base textstyle uncramped"><span class="mord mathit" style="margin-right:0.10903em;">N</span></span></span></span> 个实数，数字间以一个空格分隔。</p>
<h3 id="-">输出格式：</h3>
<p>对每个非法输入，在一行中输出 <code>ERROR: X is not a legal number</code>，其中 <code>X</code> 是输入。最后在一行中输出结果：<code>The average of K numbers is Y</code>，其中 <code>K</code> 是合法输入的个数，<code>Y</code> 是它们的平均值，精确到小数点后 2 位。如果平均值无法计算，则用 <code>Undefined</code> 替换 <code>Y</code>。如果 <code>K</code> 为 1，则输出 <code>The average of 1 number is Y</code>。</p>
<h3 id="-1-">输入样例 1：</h3>
<pre><code class="lang-in">7
5 -3.2 aaa 9999 2.3.4 7.123 2.35
</code></pre>
<h3 id="-1-">输出样例 1：</h3>
<pre><code class="lang-out">ERROR: aaa is not a legal number
ERROR: 9999 is not a legal number
ERROR: 2.3.4 is not a legal number
ERROR: 7.123 is not a legal number
The average of 3 numbers is 1.38
</code></pre>
<h3 id="-2-">输入样例 2：</h3>
<pre><code class="lang-in">2
aaa -9999
</code></pre>
<h3 id="-2-">输出样例 2：</h3>
<pre><code class="lang-out">ERROR: aaa is not a legal number
ERROR: -9999 is not a legal number
The average of 0 numbers is Undefined
</code></pre>
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