C++PrimerPlus详解

2024-04-02 19:55

短信预约 -IT技能 免费直播动态提醒

1.各种数据类型的长度

int main(void)
{
	using namespace std;
	int n(3); // C++还可以这么赋值
	int m{6};
	int f = {8};
	int n_int = INT_MAX; //声明变量同时赋值=初始化
	short n_short = SHRT_MAX;
	long n_long = LONG_MAX;
	long long n_llong = LLONG_MAX;
	cout << "n = " << n << endl;
	cout << "m = " << m << endl;
	cout << "f = " << f << endl;
	cout << "int is " << sizeof(int) << " bytes." << endl;		// sizeof是运算符不是clmits中的函数.INT_MAX是
	cout << "short is " << sizeof n_short << " bytes." << endl; //函数必须带括号，sizeof(运算符)在这里可以不跟括号，但查看数据类型必须加括号
	cout << "long is " << sizeof n_long << " bytes." << endl;
	cout << "long long is " << sizeof n_llong << " bytes." << endl;
	cout << "Maximum values: " << endl;
	cout << "int: " << n_int << endl;
	cout << "short: " << n_short << endl;
	cout << "long: " << n_long << endl;
	cout << "long long: " << n_llong << endl;
	return 0;
}

2. 无符号数据类型及cout进制显示

2.1 无符号数据类型及溢出

#include <iostream>
#include <climits> //可以查看数据类型最大值最小值
int main(void)
{
	using namespace std;
	short sam = SHRT_MAX;	  //-32768-32767 （16位）   longlong > long（至少32位）> int > short（至少16位）
	unsigned short sue = sam; // 0-65535
	cout << "sam has " << sam << " dolloars and sue has " << sue << " dolloars" << endl;
	cout << "Add 1 dolloars to each account" << endl;
	sam = sam + 1;
	sue = sue + 1;
	cout << "Now sam has " << sam << " dolloars and sue has " << sue << " dolloars" << endl;
	sam = 0;
	sue = 0;
	sam = sam - 1;
	sue = sue - 1;
	cout << "Now sam has " << sam << " dolloars and sue has " << sue << " dolloars" << endl;
	return 0;
}

2.2 cout十六进制显示

#include <iostream>
int main(void)
{
	using namespace std;
	int cheat = 42;	  //十进制
	int waist = 0x42; //十六进制
	int inseam = 042; //八进制
	cout << hex; //修改cout显示整数的方式
	cout << "cheat = " << cheat << " 42 (in decimal)" << endl;
	cout << "waist = " << waist << " 0x42 (in hexadicimal)" << endl;
	cout << "inseam = " << inseam << " 042 (in octal)" << endl; // cout默认以十进制显示整数
	return 0;
}

2.3 cout 八进制十进制十六进制显示

#include <iostream>
int main(void)
{
	using namespace std;
	int cheat = 42;
	int waist = 0x42;
	int inseam = 042;
	cout << "cheat = " << cheat << " 42 (in decimal)" << endl; // cout默认十进制显示
	cout << hex; //修改cout为十六进制显示
	cout << "waist = " << waist << " 0x42 (in hexadicimal)" << endl;
	cout << oct; //修改cout为八进制显示
	cout << "inseam = " << inseam << " 042 (in octal)" << endl;
	return 0;
}

3.char、ASCII、\n

3.1 char类型

#include <iostream>
int main(void)
{
	using namespace std;
	char ch;
	cout << "Enter a character:" << endl;
	cin >> ch;    //cin将键盘输入的M转换为77
	cout << "Hello, thanks you for the " << ch << " character." << endl; //cout将77转换为M，cin和cout的行为由变量类型引导
	return 0;
}

3.2 ASCII与char、cout.put()

#include <iostream>
int main()
{
	using namespace std;
	char ch = 'M';
	int i = ch;
	cout << "The ASCII code for " << ch << " is " << i << endl;
	cout << "Add one to the character code:" << endl;
	ch = ch + 1; //显示下一个字符
	i = ch;
	cout << "The ASCII code for " << ch << " is " << i << endl;
	cout << "Displaying char ch using cout.put(ch)" << endl; // iostream类(数据以及操作数据的方法)的对象cin、cout    矩形（对象）平移（方法）
	cout.put(ch); //用对象访问类里面的操作方法（函数）、
	cout.put('!');
	cout.put('A');
	cout << "Done" << endl;
	return 0;
}

cin与cout的行为由变量引导

3.3 转义字符换行

#include <iostream>
int main(void)
{
	using namespace std;
	int n = 10;
	cout << "Hello world!" << endl;
	cout << "Good morning!\n";//使用转义字符换行,显示字符串这种方法简单一点，\n是一个字符哦（换行符）
	cout << "What's your name?" << '\n';
	cout << "What's your name?" << "\n";
	cout << "n = " << n << endl;
	cout << "n = " << n << "\n";
	return 0;
}

4.const

#include <iostream>
int main()
{
    using namespace std;
    const int toes = 10; //必须在声明时赋值（之后不准修改）（对const初始化）
    
    return 0;
}

5.浮点数（整数部分+小数部分）

#include <iostream>
int main()
{
    using namespace std;
    cout.setf(ios_base::fixed, ios_base::floatfield);
    float tub = 10.0 / 3.0;
    const float million = 1.0E6;
    cout << "tub = " << tub << endl;                             // cout默认输出小数点后六位
    cout << "A million tubs = " << million * tub << endl;        // float精度达不到
    cout << "Ten million tubs = " << 10 * million * tub << endl; // float精度达不到
    double mint = 10.0 / 3.0;
    cout << "A million mint = " << million * mint << endl;
    cout << "Ten million mint = " << 10 * million * mint << endl; // double精度比float高
    return 0;
}

6. 比较大的浮点数

#include <iostream>
int main()
{
    using namespace std;
    float a = 2.34E22; // 2.34e/E+22   2.34*10^22
    float b = a + 1.0;
    cout << "a = " << a << endl;
    cout << "b = " << b << endl;          //a = b
    cout << "b - a = " << b - a << endl; // float位数只有前六位或前七位有效
    return 0;
}

7.float与double的精度

float单精度至少32位 double双精度至少48位

浮点数在内存中如何存储的？ int 类型 5 以0101二进制存储这个好理解

float 8.25 单精度内存中32位（bit） double 64位计算机存浮点数都是以科学计数法的方式存储的 IEEE标准

8.25 科学计数法 8.25 * 10^0 112.5 科学计数法 1.125 * 10^2 十进制的科学计数法但是计算机只认识二进制的科学计数法

8.25 二进制的科学计数法(分成整数部分（倒序）+小数部分（正序）) 1000.01 转换为科学计数法为1.00001*2^3

50.25 整数部分（32+16+2） 110010.01 任何一个浮点数二进制科学计数法为 1.？？？？？*2^x 整数部分一定为1

符号占1bit 正数为 0，负数为 1； 1.00001*2^3 指数3表示小数点右移

0 - 255 中间127 0-126（负次幂） 127-255（代表正次幂）

8.25在内存中的表示：符号位0 8位指数位为127+3=130（3次幂） 130 -- 10000010 0（符号位） 10000010（指数位） 00001（小数位，23位） 000000000000000000（18个0）

整数部分1位，小数部分23位，共24位（二进制） 4位对应一个十进制的数 24/4=6 对应十进制有效位6位二进制32位课本56页

double类型：十进制13（52/4）位有效位二进制64位符号位1 指数位11 小数位 52

11.17 二进制 1011.001010111100001........(小数部分很难取整，无限长 ) 而float最多表示32位小数部分，二进制超过32位就不对了，十进制超过6位就不对了

26.0在内存中如何存储的？ 0100000110100000............

11010.00000000............

1.10100.......0 * 2 ^ 4

符号位：0 指数位：127 + 4 = 131 二进制：10000011 小数位：010000000000...........

0.75 二进制 0.110000.............

1.10*(2^-1)

符号位：0 指数位：127 + (-1) = 126 二进制：01111110 小数位：1000000000...........

-2.5 二进制 10.1

-1.01*2^1

符号位：1 指数位：127 + 1 = 128 二进制：10000000 小数位：0100000000...........

8.float的误差


// 26.0在内存中如何存储的？ 11010.00000000............ 1.10100.......0 * 2 ^ 4 符号位：0 指数位：127 + 4 = 131 二进制：10000011 小数位：010000000000...........
#include <iostream>
int main(void)
{
    using namespace std;
    float hats, heads;
    cout.setf(ios_base::fixed, ios_base::floatfield); //可以强制打印小数点后六位（没办法四舍五入）,去掉这一句就可以四舍五入，输出61.42000000.......0可以不显示
    cout << "Enter a number: "; // 50.25
    cin >> hats;
    cout << "Enter another number: "; // 11.17
    cin >> heads;
    cout << "hats = " << hats << " heads = " << heads << endl;
    cout << "hats + heads = " << hats + heads << endl; // 61.42  的小数部分 0.42 二进制01101...........无限，但是float二进制小数部分只有23位有效，十进制六位61.4199（近似有效）
    cout << "hats - heads = " << hats - heads << endl;
    cout << "hats * heads = " << hats * heads << endl;
    cout << "hats / heads = " << hats / heads << endl; // folat精度不够，二进制只能显示小数点后23位，所以不准，去掉setf（）可四舍五入
    return 0;
}

注视掉 cout.setf()

解决办法：用double 可显示二进制小数点后53位，十进制13位，我们用setf()显示6位显然也是准确的

9.乘除法

#include <iostream>
int main(void)
{
    using namespace std;
    cout.setf(ios_base::fixed, ios_base::floatfield); //显示小数点后六位
    cout << "Integer division : 9/5 = " << 9 / 5 << endl; //整数相除结果取出整数部分
    cout << "Float division : 9.0/5.0 = " << 9.0 / 5.0 << endl;
    cout << "Mixed division : 9.0/5 = " << 9.0 / 5 << endl; //混合类型
    cout << "Mixed division : 9/5.0 = " << 9 / 5.0 << endl; //混合类型  浮点型精度高于整型，提升精度为浮点型
    cout << "Double division : 1e7 / 9.0 = " << 1e7 / 9.0 << endl;              //都当成double类型来处理(精度高) 一般定义浮点数用double，编译器默认当成double处理，除非你强制float
    cout << "FLoat constance division : 1e7f / 9.0f = " << 1e7f / 9.0f << endl; //都当成float类型来处理
    return 0;
}

10.求模运算符

#include <iostream>
int main(void)
{
    using namespace std;
    const int pounds_per_stone = 14; //声明整型类型常量   14榜(pounds)=1英石(stone)
    cout << "Enter your weight in pounds: ";
    int lbs;
    cin >> lbs;
    int stone = lbs / pounds_per_stone;
    int pounds = lbs % pounds_per_stone;
    cout << lbs << "pounds = " << stone << " stone, " << pounds << " pounds." << endl;
    return 0;
}

11.数值转换

#include <iostream>
int main(void)
{
    using namespace std;
    cout.setf(ios_base::fixed, ios_base::floatfield);
    float tree = 3;
    int guess(3.9832); // C++特有赋值方式,这里取出小数的整数部分
    int debt = 6.2E22; //超过了整型的取值范围,结果不确定，对于int（32位 -2^31---2^31-1）太大了
    cout << "tree = " << tree << endl;
    cout << "guess = " << guess << endl;
    cout << "debt = " << debt << endl;
    return 0;
}

12.强制类型转换

 
#include <iostream>
int main(void)
{
    using namespace std;
    int auks, bats, coots;
    auks = 19.99 + 11.99;            //计算机用double类型相加计算再转换为整型，结果取整=31
    bats = (int)19.99 + (int)11.99;  // C语言格式
    coots = int(19.99) + int(11.99); // C++语言格式
    cout << "auks = " << auks << endl;
    cout << "bats = " << auks << endl;
    cout << "coots = " << auks << endl;
    char ch = 'Z';
    cout << "The code for " << ch << " is " << int(ch) << endl;
    cout << static_cast<int>(ch) << endl; //强制类型转换
    return 0;
}