20240405，数据类型，运算符，程序流程结构

时间：2024-04-06 08:44:52

是我深夜爆炸，不能再去补救C了，真的来不及了，不能再三天打鱼两天晒网了，真的来不及了呜呜呜呜

我实在是不知道看什么课，那黑马吧……MOOC的北邮的C++正在进行呜呜

#include <iostream>
using namespace std;
int main() 
{
	cout << "hallo world" << endl;
	system("pause");
	return 0;
}
1.1  变量

定义变量：数据类型  变量名称 = 变量初始值【格式】

1.2  常量  不可修改

1，#define 宏常量，#define 常量名  常量值
2，const  修饰的变量  ，const  数据类型 常量名=常量值

#include <iostream>
#define DAY 7
using namespace std;
int main() 
{
	const int mouth = 31;
	cout << "hallo world,一周"<<DAY<<"天，大月"<<mouth << endl;
	system("pause");
	return 0;
}
1.3  关键字

标识符命名规则：非关键字，字母+数字+下划线，首位非数字，大小写
建议，最好能够见名知意

二，数据类型

2.1  整型

short ==2 【-32768~32767】;int ==4;long==4（分那啥）;long long==8;
sizeof( )

#include <iostream>
using namespace std;
int main() 
{
	short num1 = 32768;
	int num2 = 32768;
	long num3 = 0;
	long long num4 = 0;
	cout << num1 << "——"<<sizeof(short)<<endl;
	cout << num2 << "——" << sizeof(int) << endl;
	cout << num3 << "——" << sizeof(long) << endl;
	cout << num4 << "——" << sizeof(long long) << endl;
	system("pause");
	return 0;
}
2.2  实型（浮点型

float 单精度，7有效数字，数值后面加上F表示类型；double，双。。，15-16位
默认输出6位小数，科学计数法

#include <iostream>
using namespace std;
int main() 
{
	float fnum1 = 3.15344534f;//加后缀自动识别FLOAT，否则DOUBLE
	double dnum2 = 4.4335363748456345234232;
	float num3 = 3e2;
	float num4 = 3e-2;
	cout << fnum1 << "——"<<sizeof(float)<<endl;
	cout << dnum2 << "——" << sizeof(double) << endl;
	cout << num3 << endl;
	cout << num4 << endl;
	system("pause");
	return 0;
}
 2.3  字符型

CHAR  变量名 =‘单个字符’，大小1字节，ASCII码，a-97，A-67，0-31控制字符，32-126打印字符

#include <iostream>
using namespace std;
int main() 
{
	char a = 'a';
	cout << a << "——"<<sizeof(char)<<endl;
	cout << a << "——" << (int)a << endl;
	system("pause");
	return 0;
}
2.4 转义字符

水平制表符——对齐、整齐输出，换页和垂直制表感觉和换行差不多

#include <iostream>
using namespace std;
int main()
{
	cout << "aaa\abbb" << endl;
	cout << "aaa\bbb" << endl;
	cout << "aaa\f换页bbb" << endl;
	cout << "aaa\nbbb" << endl;
	cout << "aaa\tbbb" << endl;
	cout << "a\tbbb" << endl;
	cout << "aaa\vbbb\v垂直制表" << endl;
	cout << "aaa\vbbb\v垂直制表" << endl;
	cout << "aaa\\bbb" << endl;
	cout << "aaa\'bbb" << endl;
	cout << "aaa\"bbb" << endl;
	cout << "aaa\?bbb" << endl;
	return 0;
	system("pause");
}
2.5 字符串型

1，C风格字符串：CHAR 变量名【】=“字符串值”；CHAR A='A'字符，CHAR A[ ]="A"字符串
2，C++风格字符串：STRING 变量名=“字符串值”；；包含头文件#include <string>

#include <iostream>
#include <string>
using namespace std;
int main()
{
	char a[] = "hallo word?";
	string b = "ni hao,xiexie";
	cout << a << endl;
	cout << b << endl;
	return 0;
	system("pause");
}
2.6 布尔类型BOOL

true--1,false--0,sizeof(bool)==1;赋值给数字，除了0都代表真

#include <iostream>
using namespace std;
int main()
{
	bool flag = true;
	cout << flag << endl;
	flag = false;
	cout << flag << endl;
	cout << sizeof(bool) << endl;//1
	return 0;
	system("pause");
}
2.7 数据输入
#include <iostream>
#include<string>
using namespace std;
int main()
{
	//int
	int ant = 23;
	cout << ant << endl;
	cin >> ant;
	cout << ant << endl;

	//float
	float ff = 5.8900f;
	cout << ff << endl;//输出抹零了
	cin >> ff;
	cout << ff << endl;

	//char
	char ch = 'a';
	cout << ch << endl;
	cin >> ch;
	cout << ch << endl;

	//string
	string b= "qunidsefw";
	cout << b << endl;
	cin >> b;
	cout << b << endl;

	//bool
	bool flag = false;
	cout << flag << endl;//除了0，输入啥都是1
	cin >> flag;
	cout << flag << endl;

	return 0;
	system("pause");
}

三，运算符

3.1 算数运算符

+，-，*，/，%【小数和小数不能做取余运算】，++A，A++，--A，A--，同C

#include <iostream>
using namespace std;
int main()
{
	int a = 2;
	int b = a++;
	int c = ++a;
	cout << a << "\t" << b << "\t" << c << endl;
	cout << c % a << endl;
	cout << a++ * 100 << endl;
	cout << ++a * 100 << endl;
	return 0;
	system("pause");
}
3.2 赋值运算符

+=，-=，*=，/=，=，%=

3.3 比较运算符

==，！=，<，>，<=，>=

#include <iostream>
using namespace std;
int main()
{
	int a = 2;
	int b = ++a;
	cout << (a>b)<< endl;
	cout << (a < b) << endl;
	cout << (a != b) << endl;
	cout << (a==b)<< endl;
	cout << (a <= b) << endl;
	cout << (a >= b) << endl;
	return 0;
	system("pause");
}
3.4 逻辑运算符

！非【BOOL里面，不是0都是真】，&&与，||或

#include <iostream>
using namespace std;
int main()
{
	int a = 2; int b = 10;
	cout << !a << endl;
	cout << !!a << endl;
	a = 2; b = 2;
	cout << (a&&b)<< endl;
	cout << (a || b) << endl;
	a = 0; b = 3;
	cout << (a && b) << endl;
	cout << (a || b) << endl;
	a = 0; b = 0;
	cout << (a && b) << endl;
	cout << (a || b) << endl;
	return 0;
	system("pause");
}

四，程序流程结构

顺序，选择，循环 
【C撸了不少了，就不仔细打了】

4.1 选择结构

1.0  IF——同C
2.0 三目运算符：表达式？A：B，如果表达式为真，返回A，假返回B【返回的是变量，可以继续赋值】
3.0 SWITCH——同C【结构清晰，效率高，只能整型和字符型，BREAK】

#include <iostream>
using namespace std;
int main()
{
	int a = 9, b = 90;
	cout << (a > b ? a : b) << endl;
	(a > b ? a : b) = 78;//==78
	cout << a << endl;
	cout << b << endl;
	(a < b ? a : b) = 78;
	cout << a << endl;
	cout << b << endl;
	return 0;
	system("pause");
}
4.2 循环结构

1.0 WHILE循环
【RAND()%100,%100表示生成随机数的区间，0~99，0+1~99+1,rand()%100+1】
可以用BREAK退出当前循环
2.0 DO……WHILE循环

#include <iostream>
#include<ctime>
using namespace std;
int main()
{
	srand((unsigned int)time(NULL));
	//添加随机数种子，作用：利用当前系统时间生成随机数，防止每次随机数都一样
	int num=rand() % 100 + 1;
	cout << "请猜数字" << endl;
	int val;
	cin >> val;
	while(num!=val)
	{
		if (num > val)
		{
			cout << "猜小了" << endl;
		}
		else if (num < val)
		{
			cout << "猜大了" << endl;
		}
		cin >> val;
	}
	cout << "恭喜猜对了，数字就是" <<val<< endl;
	return 0;
	system("pause");
}
#include <iostream>
#include<ctime>
using namespace std;
int main()
{
	int a = 0;
	do
	{
		cout << a << endl;
		a++;
		if (a == 10)break;
	} while (a);

	a = 0;
	while (a)
	{
		cout << a << endl;
		a++;
		if (a == 10)
		{
			break;
		}
	}
	return 0;
	system("pause");
}

3.0 FOR循环
​​​​​​​4.0 嵌套循环——外层执行一次，内层执行一周

#include <iostream>
#include<ctime>
using namespace std;
int main()
{
	for (int i = 0; i < 10; i++)
	{
		for (int i = 0; i < 10; i++)
		{
			cout << "* ";
		}
		cout << endl;
	}
	return 0;
	system("pause");
}

4.3 跳转语句

1.0 break语句，跳出循环，嵌套循环中可以是跳出内循环

2.0 continue语句，结束本次，继续下一次循环

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