C++Primer第五版 5.3.2节练习

练习5.9：编写一段程序，使用一系列if语句统计从cin读入的文本中有多少个元音字母。

练习5.10：我们之前实现的统计元音字母的程序存在一个问题：如果元音字母以大写字母形式出现，不会被统计在内。编写一段程序，既统计元音字母的小写形式，也统计大写形式，也就是说，新程序遇到‘a’和‘A’都应该递增aCnt的值，以此类推。

练习5.11：修改统计元音字母的程序，使其也能统计空格，制表符和换行符的数量。

练习5.12：修改统计元音字母的程序，使其能统计以下含有两个字符的字符序列的数量：ff，fl和fi。

答：练习5.9-5.12见云盘程序。

练习5.13：下面显示的每个程序都含有一个常见的编程错误，指出错误在哪里，然后修改它们。

（a）.
 unsigned aCnt = 0, eCnt = 0, iouCnt = 0;
      char ch = next_text();
      switch (ch) {
      case ‘a’ : aCnt++;//缺少break 
      //break;
case ‘e’ : eCnt++;//缺少break
      //break;
default: iouCnt++;//缺少break
//break;
}
(b). 
unsigned index = some_value();
    Switch(index) {
case 1:
        //int ix = get_value(); // 错误：控制流绕过一个显式初始化的变量
        //ivec[ ix ] = index;  // 错误：控制流绕过一个显式初始化的变量
        break;
//break;
 default:
        ix = ivec.size() – 1;
    ivec [ ix ] = index;
}
(c).
unsigned evenCnt = 0, oddCnt = 0;
 int digit = get_num() % 10;
switch (digit)
{
 Case 1,3,5,7,9://写法错误 case 1: case 3: case 5: case 7: case 9:
  oddCnt++;
case 2,4,6,8,10://case 2: case 4: case 6: case 8: case 10:
  evenCnt++;
 break;
}

(d). unsigned ival = 512, jval = 1024, kval = 4096;
unsigned bufsize;
unsigned swt = get_bufCnt();
switch(swt)
{
case ival://错误：case标签必须是整型常量表达式。
   bufsize = ival * sizeof(int);
   break;
case jval: //错误：case标签必须是整型常量表达式。
      bufsize = javl * sizeof(int);
case kval: //错误：case标签必须是整型常量表达式。
      bufsize = kval * sizeof(int);
      break; 
}

练习5.9

#include <iostream>

using namespace std;

int main()
{
    unsigned aCnt = 0, eCnt = 0, iCnt = 0, oCnt = 0, uCnt = 0, totalCnt = 0;
    char ch;
    while (cin >> ch)
    {
        if (ch == 'a')
            ++aCnt;
        if (ch == 'e')
            ++eCnt;
        if (ch == 'i')
            ++iCnt;
        if (ch == 'o')
            ++oCnt;
        if (ch == 'u')
            ++uCnt;
        totalCnt = aCnt + eCnt + iCnt + oCnt + uCnt ;   
    } 
    cout << "a:" << aCnt << endl;
    cout << "e:" << eCnt << endl;
    cout << "i:" << iCnt << endl;
    cout << "o:" << oCnt << endl;
    cout << "u:" << uCnt << endl;
    cout << "total:" << totalCnt << endl; 
    return 0;
}

练习5.10

#include <iostream>

using namespace std;

int main()
{
    unsigned aCnt =0, eCnt = 0, iCnt = 0, oCnt = 0, uCnt = 0, other = 0, vowelCnt = 0,total = 0;
    char ch;
    while (cin >> ch)
    {
        switch (ch)
        {
            case 'a':
            case 'A': 
                ++aCnt;
                break; 
            case 'e':
            case 'E': 
                ++eCnt;
                break;
            case 'i':
            case 'I': 
                ++iCnt;
                break;
            case 'o':
            case 'O': 
                ++oCnt;
                break;
            case 'u':
            case 'U': 
                ++uCnt;
                break;
            default:
                ++other;
                break;   
        }

    }
        vowelCnt = aCnt + eCnt + iCnt + oCnt + uCnt;
        total = vowelCnt + other;   
        cout << "a:" << aCnt << endl;
        cout << "e:" << eCnt << endl;
        cout << "i:" << iCnt << endl;
        cout << "o:" << oCnt << endl;
        cout << "other:" << other << endl;
        cout << "vowelCnt:" << vowelCnt << endl;
        cout << "total:" << total << endl;
    return 0;
}

练习5.11

#include <iostream>
#include <vector>
#include <fstream>
using namespace std;

int main()
{
    unsigned aCnt =0, eCnt = 0, iCnt = 0, oCnt = 0, uCnt = 0, other = 0, vowelCnt = 0,total = 0, space = 0, tableSign = 0, Enter = 0;
    vector<char> charVector;
    char ch;
    //while (cin >> ch && ch != '#') 
    //输入流会掠过，空格，制表符，以及回车 
     ifstream in("练习5-11.txt");  
     //这边参考网上的例子，定义一个文件流，在文件同目录下，相应建一个new.txt文件，用于读取文件里的东西 
     if (!in)
     {
        cerr << "oh , shit!" << endl;
        return -1; 
     }
     while(in.get(ch))
     {
        cout << ch ;
        charVector.push_back(ch);
     }

     cout << endl;//以上打印文件里面的字符 

    for ( auto i = 0; i != charVector.size(); ++i)
    {
        switch (charVector[i])
        {
            case 'a':
            case 'A': 
                ++aCnt;
                break; 
            case 'e':
            case 'E': 
                ++eCnt;
                break;
            case 'i':
            case 'I': 
                ++iCnt;
                break;
            case 'o':
            case 'O': 
                ++oCnt;
                break;
            case 'u':
            case 'U': 
                ++uCnt;
                break;
            case ' ':
                ++space;
                break;
            case '\t':
                ++tableSign;
                break;
            case '\n':
                ++Enter;
                break; 
            default:
                ++other;
                break;   
        }
    }

        vowelCnt = aCnt + eCnt + iCnt + oCnt + uCnt;
        total = vowelCnt + other;   
        cout << "a:" << aCnt << endl;
        cout << "e:" << eCnt << endl;
        cout << "i:" << iCnt << endl;
        cout << "o:" << oCnt << endl;
        cout << "other:" << other << endl;
        cout << "vowelCnt:" << vowelCnt << endl;
        cout << "space:" << space << endl;
        cout << "tableSign:" << tableSign << endl;
        cout << "Enter:"  << Enter << endl;
        cout << "total:" << total << endl;
    return 0;
} 

练习5-11.txt
a b c d e f g h i j k l m n 
o p q

练习5.12

#include <iostream>
#include <vector>
#include <fstream>
using namespace std;

int main()
{
    unsigned aCnt =0, eCnt = 0, iCnt = 0, oCnt = 0, uCnt = 0, other = 0, vowelCnt = 0,total = 0, space = 0, tableSign = 0, Enter = 0, ffCnt = 0, flCnt = 0, fiCnt = 0;
    vector<char> charVector;
    char ch;
    //while (cin >> ch && ch != '#') 输入流会掠过，空格，制表符，以及回车 
//这边参考网上的例子，定义一个文件流，在文件同目录下，相应建一个new.txt文件，用于读取文件里的东西 
     if (!in)
     {
        cerr << "oh , shit!" << endl;
        return -1; 
     }
     while(in.get(ch))
     {
        cout << ch ;
        charVector.push_back(ch);
     }

     cout << endl;//以上打印文件里面的字符 

    for ( auto i = 0; i != charVector.size(); ++i)
    {
        switch (charVector[i])
        {
            case 'a':
            case 'A': 
                ++aCnt;
                break; 
            case 'e':
            case 'E': 
                ++eCnt;
                break;
            case 'i':
            case 'I': 
                ++iCnt;
                break;
            case 'o':
            case 'O': 
                ++oCnt;
                break;
            case 'u':
            case 'U': 
                ++uCnt;
                break;
            case ' ':
                ++space;
                break;
            case '\t':
                ++tableSign;
                break;
            case '\n':
                ++Enter;
                break; 
            case 'f':
                if (charVector[i+1] == 'f') 
                //前一个字符为f，紧接着为ff情况 
                    ++ffCnt;
                else if (charVector[i+1] == 'l')
                    ++flCnt;
                    else if (charVector[i+1] == 'i')
                        ++fiCnt;
                       //else ;
//执行一个空语句，代表上述三种情况之外的，执行一个空语句，无任何结果 
                break;
            default:
                ++other;
                break;   
        }
    }

        vowelCnt = aCnt + eCnt + iCnt + oCnt + uCnt;
        total = vowelCnt + other;   
        cout << "a:" << aCnt << endl;
        cout << "e:" << eCnt << endl;
        cout << "i:" << iCnt << endl;
        cout << "o:" << oCnt << endl;
        cout << "other:" << other << endl;
        cout << "vowelCnt:" << vowelCnt << endl;
        cout << "space:" << space << endl;
        cout << "tableSign:" << tableSign << endl;
        cout << "Enter:"  << Enter << endl;
        cout << "ffCnt:" << ffCnt << endl;
        cout << "flCnt:" << flCnt << endl;
        cout << "fiCnt:" << fiCnt << endl; 
        cout << "total:" << total << endl;
    return 0;
}