P155
练习5.1
空语句是只含一个分号的语句，表示当前什么也不做。
在程序的某个地方，语法上需要一条语句但是逻辑上不需要，此时应该使用空语句。
练习5.2
块就是用花括号括起来的（可能为空的）语句和声明的序列，一个块就是一个作用域。
在程序的某些地方，语法上需要一条语句，但是逻辑上需要多条语句，则应该使用复合语句。
练习5.3
会降低代码的可读性
while(a > 1)
sum += a ，a--;
P156
练习5.4
其他代码也需要访问控制变量时，变量需要定义在语句的外部
(a)：iter变量未初始化，且需要定义在语句的外部
(b)：if部分无意义，在while循环中已经完成了判断
P159
练习5.5
#include "stdafx.h"
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
int i;
cin >> i;
if (i > 90)
{
cout << "成绩为：A" << endl;
}
else if(i > 60)
{
cout << "成绩为：B" << endl;
}
else
{
cout << "成绩为：C" << endl;
}
system("pause");
}
练习5.6
#include "stdafx.h"
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
int i;
cin >> i;
char s = 'A';
s = i < 60 ? 'C' : (i < 90 ? 'B' : 'A');
cout << "成绩为" << s << endl;
system("pause");
}
练习5.7
ival1 = ival2 ; //缺少一个分号使用了两条语句，需要使用花括号括起来下面的if需要换成else if=替换为==
练习5.8
悬垂else：C++规定，else与其最近的尚未匹配的if相匹配
P164
练习5.9
#include <iostream>
#include <string>
#include <vector>
using namespace std;
void main()
{
char cval;
int sum_a = 0,sum_e = 0,sum_i = 0,sum_o = 0,sum_u = 0;
while (cin >> cval)
{
if (cval == 'a')
{
sum_a++;
}
else if (cval == 'e')
{
sum_e++;
}
else if (cval == 'i')
{
sum_i++;
}
else if (cval == 'o')
{
sum_o++;
}
else if (cval == 'u')
{
sum_u++;
}
}
cout<<"元音字母a的个数为："<<sum_a<<endl;
cout<<"元音字母e的个数为："<<sum_e<<endl;
cout<<"元音字母i的个数为："<<sum_i<<endl;
cout<<"元音字母o的个数为："<<sum_o<<endl;
cout<<"元音字母u的个数为："<<sum_u<<endl;
}
练习5.10
#include <iostream>
#include <string>
#include <vector>
using namespace std;
void main()
{
char cval;
int char_a = 0,char_e = 0,char_i = 0,char_o = 0,char_u = 0;
while (cin >> cval)
{
switch (cval)
{
case 'a':
case 'A':
++char_a;
break;
case 'e':
case 'E':
++char_e;
break;
case 'i':
case 'I':
++char_i;
break;
case 'o':
case 'O':
++char_o;
break;
case 'u':
case 'U':
++char_u;
break;
}
}
cout<<"元音字母a的个数为："<<char_a<<endl;
cout<<"元音字母e的个数为："<<char_e<<endl;
cout<<"元音字母i的个数为："<<char_i<<endl;
cout<<"元音字母o的个数为："<<char_o<<endl;
cout<<"元音字母u的个数为："<<char_u<<endl;
}
练习5.11
#include <iostream>
#include <string>
#include <vector>
using namespace std;
void main()
{
char cval;
int char_a = 0, char_e = 0, char_i = 0, char_o = 0, char_u = 0, sum_space = 0, sum_table = 0, sum_newline = 0;
while (cin >> std::noskipws >> cval) // 此处的std::noskipws表示的是不忽略任何地方的空白（包括制表符和空格等）
{
switch (cval)
{
case 'a':
case 'A':
++char_a;
break;
case 'e':
case 'E':
++char_e;
break;
case 'i':
case 'I':
++char_i;
break;
case 'o':
case 'O':
++char_o;
break;
case 'u':
case 'U':
++char_u;
break;
case ' ':
++sum_space;
break;
case '\t':
++sum_table;
break;
case '\n':
++sum_newline;
break;
}
}
cout << "元音字母a的个数为：" << char_a << endl;
cout << "元音字母e的个数为：" << char_e << endl;
cout << "元音字母i的个数为：" << char_i << endl;
cout << "元音字母o的个数为：" << char_o << endl;
cout << "元音字母u的个数为：" << char_u << endl;
cout << "空格的个数为：" << sum_space << endl;
cout << "制表符的个数为：" << sum_table << endl;
cout << "换行符的个数为：" << sum_newline << endl;
}
练习5.12
#include "stdafx.h"
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string sIn = "";
int nNnmff = 0, nNumfl = 0, nNumfi = 0;
string sff = "ff";
string sfl = "fl";
string sfi = "fi";
while (getline(cin, sIn))
{
if (sIn == sff)
{
++nNnmff;
}
else if (sIn == sfl)
{
++nNumfl;
}
else if (sIn == sfi)
{
++nNumfi;
}
cout << nNnmff << " " << nNumfi << " " << nNumfl << endl;
}
system("pause");
}
练习5.13
每个case和default后面都没有break ix超出了作用域每个case只能对应一个值 case后面的对应值应为一个常量，可以加const修饰符，将ival、jval、kval变成常量
P166
练习5.14
#include<iostream>
#include<string>
#include<vector>
#include <iostream>
#include <string>
#include <vector>
using namespace std;
void main()
{
string My_string, before_string, max_repeatstring;
int repeat_number = 0, flag = 0;
while (cin >> My_string)
{
if (My_string == before_string)
{
++repeat_number;
}
else
{
repeat_number = 1;
before_string = My_string;
}
if (flag < repeat_number)
{
flag = repeat_number;
max_repeatstring = before_string;
}//设置flag,max_repeatstring用来保存当前比较完字符串后的最大重复次数和对应字符串
}
if (flag == 1)
{
cout << "没有重复的字符串出现" << endl;
}
else
{
cout << "单词" << max_repeatstring << "出现了" << flag << "次" << endl;
}
}
P168
练习5.15
ix应该在循环外定义缺少一个;号++sz，永远也结束不了
练习5.16
更倾向于用for，因为可以准确取到某个位置的值
练习5.17
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
bool bIs = false;
vector <int> vec1 = { 0,1,1,2 };
vector <int> vec2 = { 0,1,1,2,3,5,8 };
int size1 = vec1.size();
int size2 = vec2.size();
int realSize = size1 > size2 ? size2 : size1;
for (int i = 0; i < realSize; i++)
{
if (vec1.at(i) == vec2.at(i))
{
continue;
}
bIs = true;
}
if (bIs)
{
cout << "不存在前缀关系" << endl;
}
else
{
cout << "是前缀关系" << endl;
}
system("pause");
}
P170
练习5.18
do后面那么多条语句，需要使用花括号因为do循环体中肯定还需要使用到ival这个变量，所以应该将其定义在循环体外部ival超出了作用域
练习5.19
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
cout << "请输入两个字符串：";
string str1, str2;
do
{
int size1 = str1.size();
int size2 = str2.size();
if (size1 < size2)
{
cout << str1 << endl;
}
else
{
cout << str2 << endl;
}
} while (cin >> str1 >> str2);
system("pause");
}
P171
练习5.20
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string str;
vector<string> strVec;
int nPos = -1;
while (cin >> str)
{
strVec.push_back(str);
int nSize = strVec.size();
for (int i = 0; i < nSize - 1; i++)
{
if (str == strVec.at(i))
{
nPos = i;
}
}
if (nPos > 0)
{
break;
}
}
if (nPos > 0)
{
cout << "重复的是：" << str << endl;
}
system("pause");
}
练习5.21
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
string str;
vector<string> strVec;
int nPos = -1;
while (cin >> str)
{
strVec.push_back(str);
int nSize = strVec.size();
for (int i = 0; i < nSize - 1; i++)
{
string ss = strVec.at(i);
if (str == ss && ss[0] >= 'A' && ss[0] <= 'Z')
{
nPos = i;
}
}
if (nPos > 0)
{
break;
}
}
if (nPos > 0)
{
cout << "重复的是：" << str << endl;
}
system("pause");
}
P172
练习5.22
int sz; do { sz = get_size(); } while(sz<=0)
P177
练习5.23
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
int num1, num2;
cin >> num1 >> num2;
cout << num1 / num2 << endl;
system("pause");
}
练习5.24
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
int num1, num2;
cin >> num1 >> num2;
if (num2 == 0)
{
throw runtime_error("Data Error!");
}
cout << num1 / num2 << endl;
system("pause");
}
练习5.25
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
int num1, num2;
try
{
cin >> num1 >> num2;
if (num2 == 0)
{
throw runtime_error("Data Error!");
}
cout << num1 / num2 << endl;
}
catch (runtime_error err)
{
cout << "输入错误！";
}
system("pause");
}
