C++ Primer Plus(第六版)--学习杂记（第五章）

1.

#include<iostream>
using namespace std;
int main()
{
int x;
cout<<"The expression x = 100 has the value ";
cout<<(x = 100)<<endl;
cout<<"Now x = "<<x<<endl;
cout<<"The expression x < 3 has the value ";
cout<<(x < 3)<<endl;
cout<<"The expression x > 3 has the value ";
cout<<(x > 3)<<endl;
cout.setf(ios_base::boolalpha);
cout<<"The expression x < 3 has the value ";
cout<<(x < 3)<<endl;
cout<<"The expression x > 3 has the value ";
cout<<(x > 3)<<endl;
}

cout.setf(ios_base::boolalpha)函数调用设置了一个标记，该标记命令cout显示true和false，而不是0和1

2.

对long long的应用：

#include<iostream>
using namespace std;
const int ArSize = 16;
int main()
{
long long factorials[ArSize];
factorials[1] = factorials[0] = 1LL;
for(int i=2;i<ArSize;i++)
factorials[i] = i*factorials[i-1];
for(int i=0;i<ArSize;i++)
cout<<i<<"! = "<<factorials[i]<<endl;
}

3.

倒序输出字符串

#include<iostream>
#include<string>
using namespace std;
int main()
{
cout<<"Enter a word: ";
string word;
cin>>word;
for(int i = word.size()-1;i>=0;i--)
cout<<word[i];
cout<<endl;
}

4.

前缀运算符是从右到左

++pt，pt递增后再将 作用于它

*p++后缀运算符++的优先级更高，移到右值

5.

strcmp( )函数，该函数接受两个字符串地址作为参数。这意味着参数可以是指针、字符串常量或字符数组名。如果两个字符串相同，该函数将返回零；如果第一个字符串按字母排序排在第二个字符串之前，则返回一个负数值，否则，返回整数值

用strcmp的方法：

#include<iostream>
#include<cstring>
using namespace std;
int main()
{
char word[5]="?ate";
for(char ch ='a';strcmp(word,"mate");ch++)
{
cout<<word<<endl;
word[0]=ch;
}
cout<<"After loop ends, word is "<<word<<endl;
return 0;
}

用string的方法：

#include<iostream>
#include<cstring>
using namespace std;
int main()
{
string word="?ate";
for(char ch ='a';word!="mate";ch++)
{
cout<<word<<endl;
word[0]=ch;
}
cout<<"After loop ends, word is "<<word<<endl;
return 0;
}

6.

编写延时循环

#include<iostream>
#include<cstring>
using namespace std;
int main()
{
printf("1");
long long wait=0;
while(wait<1000000000)
wait++;
printf("\n2\n");
}

这能让两个输出之间有了个时间差，另外，有些编译器可能修改上述代码，将wait改成1000000000，从而跳过该循环。

更好的办法是让系统时钟来完成这个操作

#include<iostream>
#include<ctime>
using namespace std;
int main()
{
cout<<"Enter the delay time, in seconds: ";
float secs;
cin>>secs;
clock_t delay = secs * CLOCKS_PER_SEC;
cout<<"starting\a\n";
clock_t start = clock();
while(clock()-start<delay)
;
cout<<"done \a\n";
return 0;
}

输入的数字就是那个闪闪的下划线出现的次数+1

符号常量：CLOCKS_PER_SEC，等于每秒钟包含的系统时间单位数，因此系统时间除以这个值就等于秒数。

ctime将clock_t作为clock( )返回类型的别名，这意味着可以将变量声明为clock_t类型。

7.

C++为类型建立别名有两种方式：

一种是使用预处理器：

#define BYTE char

用char替换掉所有的BYTE，BYTE是char的别名

第二种是使用关键字typedef，

typedef char byte;
//byte作为char的别名
typedef char * byte;
//byte作为char指针的别名

用typedef会更好

8.

使用最原始的cin

#include<iostream>
using namespace std;
int main()
{
char ch;
int count = 0;
cout<<"Enter character; enter # to quit:"<<endl;
cin>>ch;
while(ch!='#')
{
cout<<ch;
++count;
cin>>ch;
}
cout<<endl<<count<<" characters read"<<endl;
return 0;
}

cin在读取char值时，与读取其他基本类型一样，cin将忽略空格和换行符。因此输入中的空格没有被回显，也没有被包括在计数内。发送给cin的输入被缓冲，这意味着只有在用户按下回车键后，他输入的内容才会被发送给程序。这就是在运行该程序时，可以在#后面输入字符的原因，按下回车键，整个字符序列发送给程序，但程序在遇到#字符后将结束对输入的处理

#include<iostream>
using namespace std;
int main()
{
char ch;
int count = 0;
cout<<"Enter character; enter # to quit:"<<endl;
cin.get(ch);
while(ch!='#')
{
cout<<ch;
++count;
cin.get(ch);
}
cout<<endl<<count<<" characters read"<<endl;
return 0;
}

这个程序能计数每个字符，包括空格

9.

函数重载

10.

检查文件尾（EOF），C++输入工具和操作系统协同工作，来检测文件尾并将这种信息告诉程序。

#include<iostream>
using namespace std;
int main()
{
char ch;
int count = 0;
cout<<"Enter character; enter # to quit:"<<endl;
cin.get(ch);
while(cin.fail()==false)
{
cout<<ch;
++count;
cin.get(ch);
}
cout<<endl<<count<<" characters read"<<endl;
return 0;
}

ctrl+z+enter

(1)

cin.get(ch);

while(cin.fail()==false)

(2)

ch=cin.get();

while(ch!=EOF)

(3)

while((ch=cin.get())!=EOF)

11.

二维数组：

#include<iostream>
using namespace std;
const int Cities = 5;
const int Years = 4;
int main()
{
const char * cities[Cities]=
{
"G city",
"A city",
"N city",
"S city",
"T city"
};
int maxtemps[Years][Cities]=
{
{96,100,87,101,105},
{96,100,87,101,104},
{96,100,87,101,107},
{96,100,87,101,108},
};
cout<<"max ....... for\n\n";
for(int city = 0;city<Cities;++city)
{
cout<<cities[city]<<":\t";
for(int year=0;year<Years;++year)
cout<<maxtemps[year][city]<<"\t";
cout<<endl;
}
return 0;
}

12.

这句话的意思：

int x = (1,024);

逗号运算符，值为右边的值，024是八进制的20，因此x=20;

13.

#include <iostream>
const int MONTHS = 12;
const char* months[MONTHS]={"January","February","March","April","May","June","July","August","September","October","November","December"};
const char* years[3]={"第一年","第二年","第三年"};
int main()
{
using namespace std;
int year_sale[3],sum=0,sales[3][MONTHS];
for(int i=0;i<3;i++)
{
int temp=0;
cout<<years[i]<<"的每个月销售量:"<<endl;
for(int j=0;j<MONTHS;j++)
{
cout<<"请输入"<<months[j]<<"的销售量:";
cin>>sales[i][j];
temp+=sales[i][j];
}
year_sale[i]=temp;
sum+=year_sale[i];
}
for(int i=0;i<3;i++)
cout<<years[i]<<"的销售量为："<<year_sale[i]<<endl;
cout<<"这三年的总销售量为："<<sum<<endl;
return 0;
}

14.

#include <iostream>
#include <string>
using namespace std;
struct car{
string name;
int year;
};
int main()
{
cout<<"How many cars do you wish to catalog? ";
int num;
(cin>>num).get();
car* ps=new car[num];
for(int i=0;i<num;++i)
{
cout<<"Car #"<<i+1<<":\n";
cout<<"Please enter the make: ";
getline(cin,ps[i].name);
cout<<"Please enter the year made: ";
(cin>>ps[i].year).get();
}
cout<<"Here is your collection:\n";
for(int i=0;i<num;++i)
cout<<ps[i].year<<" "<<ps[i].name<<endl;
delete [] ps;
return 0;
}

15.

#include <iostream>
#include <cstring>

int main()
{
using namespace std;

char word[20];
int sum=0;
cout<<"Enter words (to stop,type the word done):\n";
cin>>word;
while(strcmp(word,"done"))
{
sum++;
cin>>word;
}
cout<<"You entered a total of "<<sum<<" words.\n";
return 0;
}

#include <iostream>
#include <string>

int main()
{
using namespace std;
string word;
int sum=0;
cout<<"Enter words (to stop, type the word done):\n";
cin>>word;
while(word!="done")
{
sum++;
cin>>word;
}
cout<<"You entered a total of "<<sum<<" words.\n";
return 0;
}