习题4.16 .html

c++ primer 答案（第4版） 自己整理的 只有1-5章

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //复制元素</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; int *tp = pia;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; for (vector&lt;int&gt;::iterator
iter = ivec.begin(); </p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;iter != ivec.end();
++iter, ++tp)</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; *tp =
*iter;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //释放动态数组的内存</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; delete [] pia;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; return 0;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>}</p>



<div style='border:none;border-bottom:solid #999999 1.0pt;padding:0cm 0cm 1.0pt 0cm;
margin-left:1.4pt;margin-right:1.4pt'>

<p class=aff2 style='margin-top:8.0pt;margin-right:0cm;margin-bottom:4.0pt;
margin-left:0cm;text-indent:6.0pt'>习题4.29 </p>

</div>

<p class=XT>对本节第5条框中的两段程序：</p>

<p class=XT>(a)
解释这两段程序实现的功能。</p>

<p class=XT>(b)
平均来说，使用string类型的程序执行速度要比用C风格字符串的快很多，在我们用了5年的PC机上其平均执行速度分别是：</p>



<p class=XT style='line-height:9.0pt;punctuation-trim:none'>user 0.47 # string class</p>

<p class=XT style='line-height:9.0pt;punctuation-trim:none'>user 2.55 # C-style character
string</p>



<p class=XT>你预计的也一样吗？请说明原因。</p>

<p class=aff4>【解答】</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>(a) 这两段程序的功能是：执行一个循环次数为1000000的循环，在该循环的循环体中：创建一个新字符串，将一个已存在的字符串复制给新字符串，然后比较两个字符串，最后释放新字符串。</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>(b) 使用C风格字符串的程序需要自己管理内存的分配和释放，而使用string类型的程序由系统自动进行内存的分配和释放，因此比使用C风格字符串的程序要简短，执行速度也要快一些。</p>

<div style='border:none;border-bottom:solid #999999 1.0pt;padding:0cm 0cm 1.0pt 0cm;
margin-left:1.4pt;margin-right:1.4pt'>

<p class=aff2 style='margin-top:8.0pt;margin-right:0cm;margin-bottom:4.0pt;
margin-left:0cm'>习题4.30 </p>

</div>

<p class=XT>编写程序连接两个C风格字符串字面值，把结果存储在一个C风格字符串中。然后再编写程序连接两个string类型字符串，这两个string类型字符串与前面的C风格字符串字面值具有相同的内容。</p>

<p class=aff4>【解答】</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>连接两个C风格字符串字面值的程序如下：</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>// 连接两个C风格字符串字面值，</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>// 把结果存储在一个C风格字符串中</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>#include &lt;cstring&gt;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>int main()</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>{</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; const char *cp1 = &quot;Mary and
Linda &quot;;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; const char *cp2 = &quot;are
firends.&quot;;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; size_t len = strlen(cp1) +
strlen(cp2);</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; char *result_str = new
char[len+1];</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; strcpy(result_str, cp1);</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; strcat(result_str, cp2);</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; delete [] result_str;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; return 0;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>}</p>



<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>相应的连接两个string类型字符串的程序如下：</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>// 连接两个string类型字符串</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>#include &lt;string&gt;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>using namespace std;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>int main()</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>{</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; const string str1(&quot;Mary and
Linda &quot;);</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; const string str2(&quot;are
firends.&quot;);</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; string result_str;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; result_str = str1;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; result_str += str2;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; return 0;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>}</p>



<div style='border:none;border-bottom:solid #999999 1.0pt;padding:0cm 0cm 1.0pt 0cm;
margin-left:1.4pt;margin-right:1.4pt'>

<p class=aff2 style='margin-top:8.0pt;margin-right:0cm;margin-bottom:4.0pt;
margin-left:0cm'>习题4.31 </p>

</div>

<p class=XT>编写程序从标准输入设备读入字符串，并把该串存放在字符数组中。描述你的程序如何处理可变长的输入。提供比你分配的数组长度长的字符串数据测试你的程序。</p>

<p class=aff4>【解答】</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>// 从标准输入设备读入字符串，并把该串存放在字符数组中</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>#include &lt;iostream&gt;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>#include &lt;string&gt;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>#include &lt;cstring&gt;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>using namespace std;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>int main()</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>{</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; string in_str;// 用于读入字符串的string对象</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; const size_t str_size = 10;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; char result_str[str_size+1];</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; // 读入字符串</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; cout &lt;&lt; &quot;Enter a
string(&lt;=&quot; &lt;&lt; str_size </p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;&lt;
&quot; characters):&quot; &lt;&lt; endl;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; cin &gt;&gt; in_str;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; // 计算需复制的字符的数目</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; size_t len =
strlen(in_str.c_str());</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; if (len &gt; str_size) {</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; len =
str_size;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cout
&lt;&lt; &quot;String is longer than &quot; &lt;&lt; str_size</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;&lt;
&quot; characters and is stored only &quot; </p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &lt;&lt;
str_size &lt;&lt; &quot; characters!&quot; &lt;&lt; endl;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; }</p>



<p class=MsoNormal align=left style='text-align:left;line-he