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; 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'>比较两个C风格字符串的程序如下：</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>//比较两个C风格字符串的值</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;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; //char *str1 =
&quot;string1&quot;, *str2 = &quot;string2&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 int str_size = 80;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; char *str1, *str2;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //为两个字符串分配内存</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; str1 = new char[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; str2 = new char[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; if (str1 == NULL <sub>||</sub>&nbsp;str2 == NULL) {</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;No enough memory!&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;&nbsp;&nbsp;&nbsp;&nbsp; return
-1;</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-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //输入两个字符串</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 two
strings:&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; str1 &gt;&gt; str2;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //比较两个字符串</p>

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

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; result = strcmp(str1, str2);</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; if (result &gt; 0)</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;\&quot;&quot; &lt;&lt; str1 &lt;&lt; &quot;\&quot;&quot;
&lt;&lt; &quot; is bigger than &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; &quot;\&quot;&quot; &lt;&lt; str2 &lt;&lt;
&quot;\&quot;&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; else if (result &lt; 0)</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;\&quot;&quot; &lt;&lt; str2 &lt;&lt; &quot;\&quot;&quot;
&lt;&lt; &quot; is bigger than &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;
&quot;\&quot;&quot; &lt;&lt; str1 &lt;&lt; &quot;\&quot;&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; else </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;They are equal&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; //释放字符串所占用的内存</p>

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

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



<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>注意，此程序中使用了内存的动态分配与释放（见4.3.1节）。如果不用内存的动态分配与释放，可将主函数中第2、3两行代码、有关内存分配与释放的代码以及输入字符串的代码注释掉，再将主函数中第一行代码</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>//char *str1 = &quot;string1&quot;, *str2 =
&quot;string2&quot;;</p>

<p class=MsoNormal align=left style='text-align:left;text-indent:0cm;
text-autospace:none'>前的双斜线去掉即可。</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4.26 </p>

</div>

<p class=XT>编写程序从标准输入设备读入一个string类型的字符串。考虑如何编程实现从标准输入设备读入一个C风格字符串。</p>

<p class=aff4>【解答】</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>从标准输入设备读入一个string类型字符串的程序段：</p>



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

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



<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>从标准输入设备读入一个C风格字符串可如下实现：</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>const int str_size = 80;</p>

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

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>cin &gt;&gt; str;</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4.27 </p>

</div>

<p class=XT>假设有下面的new表达式，请问如何释放pa？</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>int *pa = new int[10];</p>



<p class=aff4>【解答】</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>用语句delete [] pa;释放pa所指向的数组空间。</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4.28 </p>

</div>

<p class=XT>编写程序由从标准输入设备读入的元素数据建立一个int型vector对象，然后动态创建一个与该vector对象大小一致的数组，把vector对象的所有元素复制给新数组。</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的元素数据建立一个int型vector对象，</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>// 然后动态创建一个与该vector对象大小一致的数组，</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>// 把vector对象的所有元素复制给新数组</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;vector&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; vector&lt;int&gt; ivec;</p>

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



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //读入元素数据并建立vector</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
numbers:(Ctrl+Z to end)&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; while (cin &gt;&gt; ival)</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; ivec.push_back(ival);</p>



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

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; int *pia = new int[ivec.size()];</p>