习题5.18 .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;&nbsp;&nbsp;&nbsp;&nbsp; iter++;</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; //释放各个动态分配的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; iter = spvec.begin();</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; while (iter != spvec.end()) {</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; delete
*iter;</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; iter++;</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; 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5.19 </p>

</div>

<p class=XT>假设iter为vector&lt;string&gt;::iterator类型的变量，指出下面哪些表达式是合法的，并解释这些合法表达式的行为。</p>

<p class=MsoNormal align=left style='text-align:left;layout-grid-mode:char;
punctuation-trim:none;text-autospace:none'>(a)
*iter++; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; (b) (*iter)++;</p>

<p class=MsoNormal align=left style='text-align:left;layout-grid-mode:char;
punctuation-trim:none;text-autospace:none'>(c)
*iter.empty(); &nbsp; (d) iter-&gt;empty();</p>

<p class=MsoNormal align=left style='text-align:left;layout-grid-mode:char;
punctuation-trim:none;text-autospace:none'>(e)
++*iter; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; (f) iter++-&gt;empty();</p>



<p class=aff4>【解答】</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>(a)、(d)、(f)合法。</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>这些表达式的执行结果如下：</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>(a)返回iter所指向的string对象，并使iter加1。</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>(d)调用iter所指向的string对象的成员函数empty。</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>(f)调用iter所指向的string对象的成员函数empty，并使iter加1。</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5.20 </p>

</div>

<p class=XT>编写程序提示用户输入两个数，然后报告哪个数比较小。</p>

<p class=aff4>【解答】</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>可编写程序如下：</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>//提示用户输入两个数，然后报告哪个数比较小</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'>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; int val1, val2;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //提示用户输入两个数并接受输入</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
integers:&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; val1 &gt;&gt; val2;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //报告哪个数比较小</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;The smaller
one is&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;&lt;&lt;
(val1 &lt; val2 ? val1 : val2) &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; 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5.21 </p>

</div>

<p class=XT>编写程序处理vector&lt;int&gt;对象的元素：将每个奇数值元素用该值的两倍替换。</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'>//处理vector&lt;int&gt;对象的元素：</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>//将每个奇数值元素用该值的两倍替换</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(20,1);//ivec包含20个值为1的元素</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; //将每个奇数值元素用该值的两倍替换</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; iter !=
ivec.end(); ++iter)</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; *iter =
(*iter % 2 == 0 ? *iter : *iter * 2);</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5.22 </p>

</div>

<p class=XT>编写程序输出每种内置类型的长度。</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'>//输出每种内置类型的长度</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'>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; cout &lt;&lt;
&quot;type\t\t\t&quot; &lt;&lt; &quot;size&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; &nbsp;&lt;&lt;
&quot;bool\t\t\t&quot; &lt;&lt; sizeof(bool) &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; &nbsp;&lt;&lt;
&quot;char\t\t\t&quot; &lt;&lt; sizeof(char) &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; &nbsp;&lt;&lt;
&quot;signed char\t\t&quot; &lt;&lt; sizeof(signed char) &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; &nbsp;&lt;&lt;
&quot;unsigned char\t\t&quot; &lt;&lt; sizeof(unsigned char) &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; &nbsp;&lt;&lt;
&quot;wchar_t\t\t\t&quot; &lt;&lt; sizeof(wchar_t) &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; &nbsp;&lt;&lt;
&quot;short\t\t\t&quot; &lt;&lt; sizeof(short) &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; &nbsp;&lt;&lt;