for循环
表达式和语句
递增运算符和递减运算符：++和--
组合赋值运算符
复合语句（语句块）
逗号运算符
关系运算符：> >= == <= < !=
while循环
typedef工具
do while循环
字符输入方法get()
文件尾条件
嵌套循环和二维数组
5.1 for循环
// forloop.cpp -- introducing the for loop
#include <iostream>
int main()
{
using namespace std;
int i; // create a counter
// initialize; test ; update
for (i = 0; i < 5; i++)
cout << "C++ knows loops.\n";
cout << "C++ knows when to stop.\n";
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ forloop.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
C++ knows loops.
C++ knows loops.
C++ knows loops.
C++ knows loops.
C++ knows loops.
C++ knows when to stop.
5.1.1 for循环的组成部分
// num_test.cpp -- use numeric test in for loop
#include <iostream>
int main()
{
using namespace std;
cout << "Enter the starting countdown value: ";
int limit;
cin >> limit;
int i;
for (i = limit; i; i--) // quits when i is 0
cout << "i = " << i << "\n";
cout << "Done now that i = " << i << "\n";
// cin.get();
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ num_test.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Enter the starting countdown value: 4
i = 4
i = 3
i = 2
i = 1
Done now that i = 0
// express.cpp -- values of expressions
#include <iostream>
int main()
{
using namespace std;
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); //a newer C++ feature
cout << "The expression x < 3 has the value ";
cout << (x < 3) << endl;
cout << "The expression x > 3 has the value ";
cout << (x > 3) << endl;
/// cin.get();
return 0;
}
// express.cpp -- values of expressions
#include <iostream>
int main()
{
using namespace std;
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); //a newer C++ feature
cout << "The expression x < 3 has the value ";
cout << (x < 3) << endl;
cout << "The expression x > 3 has the value ";
cout << (x > 3) << endl;
/// cin.get();
return 0;
}
5.1.2 回到for循环
// formore.cpp -- more looping with for
#include <iostream>
const int ArSize = 16; // example of external declaration
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++)
std::cout << i << "! = " << factorials[i] << std::endl;
// std::cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ formore.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880
10! = 3628800
11! = 39916800
12! = 479001600
13! = 6227020800
14! = 87178291200
15! = 1307674368000
5.1.3 修改步长
// bigstep.cpp -- count as directed
#include <iostream>
int main()
{
using std::cout; // a using declaration
using std::cin;
using std::endl;;
cout << "Enter an integer: ";
int by;
cin >> by;
cout << "Counting by " << by << "s:\n";
for (int i = 0; i < 100; i = i + by)
cout << i << endl;
// cin.get();
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ bigstep.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Enter an integer: 12
Counting by 12s:
0
12
24
36
48
60
72
84
96
5.1.4 使用for循环访问字符串
// forstr1.cpp -- using for with a string
#include <iostream>
#include <string>
int main()
{
using namespace std;
cout << "Enter a word: ";
string word;
cin >> word;
// display letters in reverse order
for (int i = word.size() - 1; i >= 0; i--)
cout << word[i];
cout << "\nBye.\n";
// cin.get();
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ forstr1.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Enter a word: animal
lamina
Bye.
5.1.5 递增运算符（++）和递减运算符（--）
// plus_one.cpp -- the increment operator
#include <iostream>
int main()
{
using std::cout;
int a = 20;
int b = 20;
cout << "a = " << a << ": b = " << b << "\n";
cout << "a++ = " << a++ << ": ++b = " << ++b << "\n";
cout << "a = " << a << ": b = " << b << "\n";
// std::cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ plus_one.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
a = 20: b = 20
a++ = 20: ++b = 21
a = 21: b = 21
int y = ++x; //change x, then assign to y
int y = x++; //assign to y, then change z
5.1.6 副作用和顺序点
语句中的分号是一个顺序点
5.1.7 前缀格式和后缀格式
5.1.8 递增/递减运算符和指针
5.1.9 组合赋值运算符
5.1.10 复合语句（语句块）
// block.cpp -- use a block statement
#include <iostream>
int main()
{
using namespace std;
cout << "The Amazing Accounto will sum and average ";
cout << "five numbers for you.\n";
cout << "Please enter five values:\n";
double number;
double sum = 0.0;
for (int i = 1; i <= 5; i++)
{ // block starts here
cout << "Value " << i << ": ";
cin >> number;
sum += number;
} // block ends here
cout << "Five exquisite choices indeed! ";
cout << "They sum to " << sum << endl;
cout << "and average to " << sum / 5 << ".\n";
cout << "The Amazing Accounto bids you adieu!\n";
// cin.get();
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ block.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
The Amazing Accounto will sum and average five numbers for you.
Please enter five values:
Value 1: 1942
Value 2: 1948
Value 3: 1957
Value 4: 1974
Value 5: 1980
Five exquisite choices indeed! They sum to 9801
and average to 1960.2.
The Amazing Accounto bids you adieu!
5.1.11 其他语法技巧--逗号运算符
// forstr2.cpp -- reversing an array
#include <iostream>
#include <string>
int main()
{
using namespace std;
cout << "Enter a word: ";
string word;
cin >> word;
// physically modify string object
char temp;
int i, j;
for (j = 0, i = word.size() - 1; j < i; --i, ++j)
{ // start block
temp = word[i];
word[i] = word[j];
word[j] = temp;
} // end block
cout << word << "\nDone\n";
// cin.get();
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ forstr2.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Enter a word: stressed
desserts
Done
5.1.12 关系表达式
5.1.13 赋值、比较和可能犯的错误
// equal.cpp -- equality vs assignment
#include <iostream>
int main()
{
using namespace std;
int quizscores[10] =
{ 20, 20, 20, 20, 20, 19, 20, 18, 20, 20};
cout << "Doing it right:\n";
int i;
for (i = 0; quizscores[i] == 20; i++)
cout << "quiz " << i << " is a 20\n";
// Warning: you may prefer reading about this program
// to actually running it.
cout << "Doing it dangerously wrong:\n";
for (i = 0; quizscores[i] = 20; i++)
cout << "quiz " << i << " is a 20\n";
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ equal.cpp
equal.cpp:16:31: warning: using the result of an assignment as a condition without parentheses [-Wparentheses]
for (i = 0; quizscores[i] = 20; i++)
~~~~~~~~~~~~~~^~~~
equal.cpp:16:31: note: place parentheses around the assignment to silence this warning
for (i = 0; quizscores[i] = 20; i++)
^
( )
equal.cpp:16:31: note: use '==' to turn this assignment into an equality comparison
for (i = 0; quizscores[i] = 20; i++)
^
==
1 warning generated.
5.1.14 C-风格字符串的比较
word == "mate" 引号括起的字符串常量是地址
C++将C-风格视为地址
strcmp函数，可以是指针，字符串常量或字符数组名
// compstr1.cpp -- comparing strings using arrays
#include <iostream>
#include <cstring> // prototype for strcmp()
int main()
{
using namespace std;
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;
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ compstr1.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
?ate
aate
bate
cate
date
eate
fate
gate
hate
iate
jate
kate
late
After loop ends, word is mate
5.1.15 比较string类字符串
string类重载运算符！=的方式：至少有一个操作数为string对象，另一个操作数可以是string类对象，也可以是C_风格字符串。
// compstr2.cpp -- comparing strings using arrays
#include <iostream>
#include <string> // string class
int main()
{
using namespace std;
string word = "?ate";
for (char ch = 'a'; word != "mate"; ch++)
{
cout << word << endl;
word[0] = ch;
}
cout << "After loop ends, word is " << word << endl;
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ compstr2.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
?ate
aate
bate
cate
date
eate
fate
gate
hate
iate
jate
kate
late
After loop ends, word is mate
5.2 while循环
// while.cpp -- introducing the while loop
#include <iostream>
const int ArSize = 20;
int main()
{
using namespace std;
char name[ArSize];
cout << "Your first name, please: ";
cin >> name;
cout << "Here is your name, verticalized and ASCIIized:\n";
int i = 0; // start at beginning of string
while (name[i] != '\0') // process to end of string
{
cout << name[i] << ": " << int(name[i]) << endl;
i++; // don't forget this step
}
// cin.get();
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ while.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Your first name, please: Muffy
Here is your name, verticalized and ASCIIized:
u: 117
f: 102
f: 102
y: 121
5.2.1 for与while
5.2.2 等待一段时间：编写延时循环
// waiting.cpp -- using clock() in a time-delay loop
#include <iostream>
#include <ctime> // describes clock() function, clock_t type
int main()
{
using namespace std;
cout << "Enter the delay time, in seconds: ";
float secs;
cin >> secs;
clock_t delay = secs * CLOCKS_PER_SEC; // convert to clock ticks
cout << "starting\a\n";
clock_t start = clock();
while (clock() - start < delay ) // wait until time elapses
; // note the semicolon
cout << "done \a\n";
// cin.get();
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Enter the delay time, in seconds: 5
starting
done
5.3 do while循环
// dowhile.cpp -- exit-condition loop
#include <iostream>
int main()
{
using namespace std;
int n;
cout << "Enter numbers in the range 1-10 to find ";
cout << "my favorite number\n";
do
{
cin >> n; // execute body
} while (n != 7); // then test
cout << "Yes, 7 is my favorite.\n" ;
// cin.get();
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ dowhile.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Enter numbers in the range 1-10 to find my favorite number
9
5
7
Yes, 7 is my favorite.
5.4 基于范围的for循环（C++11）
5.5 循环和文本输入
5.5.1 使用原始的cin进行输入
// textin1.cpp -- reading chars with a while loop
#include <iostream>
int main()
{
using namespace std;
char ch;
int count = 0; // use basic input
cout << "Enter characters; enter # to quit:\n";
cin >> ch; // get a character
while (ch != '#') // test the character
{
cout << ch; // echo the character
++count; // count the character
cin >> ch; // get the next character
}
cout << endl << count << " characters read\n";
// get rid of rest of line
// while (cin.get() != '\n')
// ;
//cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ textin1.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Enter characters; enter # to quit:
see ken run#really fast
seekenrun
9 characters read
cin将忽略空格和换行符，因此输入的空格没有回显，被包括在计数内
进一步，发送给cin的输入被缓冲，用户只有按下回车键后，他输入的内容才会被发送给程序。
这就是运行程序时，可以在#后面输入字符的原因，按下回车键后，整个字符序列将被发送给程序，但程序在遇到#后结束对输入的处理。
5.5.2 使用cin.get(char)进行补救
// textin2.cpp -- using cin.get(char)
#include <iostream>
int main()
{
using namespace std;
char ch;
int count = 0;
cout << "Enter characters; enter # to quit:\n";
cin.get(ch); // use the cin.get(ch) function
while (ch != '#')
{
cout << ch;
++count;
cin.get(ch); // use it again
}
cout << endl << count << " characters read\n";
// get rid of rest of line
// while (cin.get() != '\n')
// ;
//cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ textin2.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Enter characters; enter # to quit:
Did you use a #2 pencil?
Did you use a
14 characters read
5.5.3 使用哪一个cin.get()
char name[ArSize];
cout << "Enter your name:\n";
cin.get(name, ArsSize).get();
cin.get(name, ArSize)；
cin.get();
char ch;
cin.get(ch);
5.5.4 文件尾条件
如果输入来自文件，可以使用功能更更大的技术--检测文件尾（EOF）
首先很多操作系统，都支持重定向，允许用文件替换键盘输入。
< 重定向运算符
操作系统支持用键盘来模拟文件尾条件 Ctrl + D（Unix）Crtl + Z（Windows）
// textin3.cpp -- reading chars to end of file
#include <iostream>
int main()
{
using namespace std;
char ch;
int count = 0;
cin.get(ch); // attempt to read a char
while (cin.fail() == false) // test for EOF
#while (!cin.fail())
{
cout << ch; // echo character
++count;
cin.get(ch); // attempt to read another char
}
cout << endl << count << " characters read\n";
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ textin3.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
The green bird sings in the winter.
The green bird sings in the winter.
^Z
[1]+ Stopped ./a.out
5.5.5 另一个cin.get()版本
// textin4.cpp -- reading chars with cin.get()
#include <iostream>
int main(void)
{
using namespace std;
int ch; // should be int, not char
int count = 0;
while ((ch = cin.get()) != EOF) // test for end-of-file
{
cout.put(char(ch));
++count;
}
cout << endl << count << " characters read\n";
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ textin4.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
The sullen mackerel sulks in the shadowy shallows
The sullen mackerel sulks in the shadowy shallows
^Z
[2]+ Stopped ./a.out
5.6 嵌套循环和二维数组
5.6.1 初始化二维数组
5.6.2 使用二维数组
// nested.cpp -- nested loops and 2-D array
#include <iostream>
const int Cities = 5;
const int Years = 4;
int main()
{
using namespace std;
const char * cities[Cities] = // array of pointers
{ // to 5 strings
"Gribble City",
"Gribbletown",
"New Gribble",
"San Gribble",
"Gribble Vista"
};
int maxtemps[Years][Cities] = // 2-D array
{
{96, 100, 87, 101, 105}, // values for maxtemps[0]
{96, 98, 91, 107, 104}, // values for maxtemps[1]
{97, 101, 93, 108, 107}, // values for maxtemps[2]
{98, 103, 95, 109, 108} // values for maxtemps[3]
};
cout << "Maximum temperatures for 2008 - 2011\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;
}
// cin.get();
return 0;
}
[wlsh@wlsh-MacbookPro] chapter_5$ g++ nested.cpp
[wlsh@wlsh-MacbookPro] chapter_5$ ./a.out
Maximum temperatures for 2008 - 2011
Gribble City: 96 96 97 98
Gribbletown: 100 98 101 103
New Gribble: 87 91 93 95
San Gribble: 101 107 108 109
Gribble Vista: 105 104 107 108
5.7 总结
