习题4.1].txt

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'>#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'>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 s1, s2;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; // 读入两个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; 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; s1 &gt;&gt; s2;</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string对象的长度</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; string::size_type len1, len2;</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; len1 = s1.size();</p>

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; len2 = s2.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 (len1 == len2)</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 have same length.&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 (len1 &gt; len2)</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; s1 &lt;&lt; &quot;\&quot; is longer
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; s2 &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;\&quot;&quot; &lt;&lt; s2 &lt;&lt; &quot;\&quot; is longer
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; s1 &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; 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3.8 </p>

</div>

<p class=XT>编一个程序，从标准输入读取多个string对象，把它们连接起来存放到一个更大的string对象中，并输出连接后的string对象。接着，改写程序，将连接后相邻string对象以空格隔开。</p>

<p class=aff4>【解答】</p>

<p class=MsoEndnoteText style='line-height:9.0pt;layout-grid-mode:both;
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'>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 result_str, str;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; // 读入多个string对象并进行连接</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 strings(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;str) </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; result_str
= result_str + str;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; // 输出连接后的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; cout &lt;&lt; &quot;String equal
to the concatenation of these strings 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;
endl &lt;&lt; result_str &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>



<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>改写后的程序：</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'>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 result_str, str;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; // 读入多个string对象并进行连接</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 strings(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; cin &gt;&gt; result_str;//读入第一个string对象，放到结果对象中</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;str) </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; result_str
= result_str + ' ' + str;</p>



<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>&nbsp;&nbsp;&nbsp; // 输出连接后的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; cout &lt;&lt; &quot;String equal
to the concatenation of these strings 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;
endl &lt;&lt; result_str &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3.9 </p>

</div>

<p class=XT>下列程序实现什么功能？实现合法吗？如果不合法，说明理由。</p>



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

<p class=MsoNormal align=left style='text-align:left;line-height:9.0pt;
punctuation-trim:none;text-autospace:none'>cout &lt;&lt; s[0] &lt;&lt; endl;</p>



<p class=aff4>【解答】</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>该程序段输出string对象s所对应字符串的第一个字符。</p>

<p class=MsoNormal align=left style='text-align:left;text-autospace:none'>实现不合法。因为s是一个空字符串，其长度为0，因此s[0]是无效的。</p>

<p class=MsoNormal align=left style='text-align:left;text-indent:19.0pt;
text-autospace:none'>注意，在一些编译器（如Microsoft Visual
C++ .NET 2003）的实现中，该程序段并不出现编译错误。</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3.10 </p>

</div>

<p class=XT>编一个程序，从string 对象中去掉标点符号。要求输入到程序的字符串必须含有标点符号，输出结果则是去掉标点符号后的string对象。</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'>#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;cctype&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>