[开发工具]c++程序设计视频学习（第二天）

2.5 转义字符

用于表示一些不能显示出来的ASCII字符

#include <iostream>
using namespace std;

int main()
{
	//转义字符

	//换行符\n
	cout << "hello world\n" ;
	
	//反斜杠 
	cout << "\\" << endl;//要打两个\\才能输出一个\
	
	//水平制表符 \t    作用：可以整齐地输出数据
	cout << "aaa\thello world" << endl;
	cout << "aaaaa\thello world" << endl;
	cout << "a\thello world" << endl;
	system("pause");
	return 0;
}

?2.6 字符串型

#include <iostream>
using namespace std;

int main()
{
	//1.C风格字符串
	//注意事项： char 字符串名 []
	//注意事项2 等号后面要用双引号
	
	char str[] = "hello world";
	cout << str << endl;
	
	//2.c++风格字符串
	string str2 = "hello world";
	cout << str2 << endl;

	system("pause");
	return 0;
}

2.7 布尔数据类型bool

布尔数据类型代表真或假两种值

1.true——真（本质是1）

2.false——假（本质是0）

bool数据类型占1个字节大小

2.8数据的输入

用于从键盘获取数据

关键字：cin

语法：cin >> 变量

#include <iostream>
using namespace std;

int main()
{
	//1.整型
	int a = 0;
	cout << "请输入整型变量a的值：" << endl;
	cin >> a;
	cout << "整型变量a = " << a << endl;

	//2.浮点型
	float f = 3.14f;
	cout << "请给浮点型变量f赋值：" << endl;
	cin >> f;
	cout << "浮点型变量f = " << f << endl;
	
	//3.字符型
	char ch = 'a';
	cout << "请给字符型变量ch赋值：" << endl;
	cin >> ch;
	cout << "字符型变量ch = " << ch << endl;
	
	//4.字符串型
	string str = "afbaob";
	cout << "请给字符串变量str赋值：" << endl;
	cin >> str;
	cout << "字符串str = " << str<<endl;
	
	//5.布尔类型
	bool flag = true;
	cout << "请给布尔类型 flag 赋值：" << endl;
	cin >> flag;
	cout << "布尔类型flag = " << flag << endl;
	
	system("pause");
	return 0;
}

3.运算符

3.1算数运算符

#include <iostream>
using namespace std;

int main()
{
	//加减乘除
	int a1 = 10;
	int b1 = 3;
	cout << a1 + b1 << endl;
	cout << a1 - b1 << endl;
	cout << a1 * b1 << endl;
	cout << a1 / b1 << endl;
	//两个整数相除，结果依然是整数，将小数部分去除

	int a2 = 10;
	int b2 = 20;
	cout << a2 / b2 << endl;
	
	int a3 = 10;
	//int b3 = 0;
	//cout << a3 / b3 << endl;
	//两个数字相除，除数是不可以为0的

	//两个小数可以相除
	double d1 = 0.5;
	double d2 = 0.22;
	cout << d1 / d2 << endl;
	//运算结果也可以是小数



	system("pause");
	return 0;
}

取模（取余）运算%

只有整型变量才可以进行取模运算

#include <iostream>
using namespace std;

int main()
{
	//取模运算本质是求余数
	int a1 = 10;
	int b1 = 3;
	cout << a1 % b1 << endl;

	int a2 = 10;
	int b2 = 20;
	cout << a2 % b2 << endl;

	int a3 = 10;
	int b3 = 0;
	//cout << a3 % b3 << endl;
	// 两个数相除，除数不能为0，因此也作不了取模运算

	//两个小数是不可以作取模运算的
	double d1 = 3.14;
	double d2 = 1.1;
	//cout << d1 % d2 << endl;

	system("pause");
	return 0;
}

递增与递减

?

#include <iostream>
using namespace std;

int main()
{
	//1.前置递增
	int a = 10;
	++a;//让变量+1
	cout << "a = " << a << endl;

	//2.后置递增
	int b = 10;
	b++;//让变量+1
	cout << "b = " << b << endl;

	//3.前置与后置的区别
	//前置递增：先让变量+1，然后进行表达式运算
	int a2 = 10;
	int b2 = ++a2 * 10;
	cout << "a2 = " << a2 << endl;
	cout << "b2 = " << b2 << endl;

	//后置递增：先进行表达式运算，后让变量+1
	int a3 = 10;
	int b3 = a3++ * 10;
	cout << "a3 = " << a3 << endl;
	cout << "b3 = " << b3 << endl;

	system("pause");
	return 0;
}

3.2 赋值运算符

作用：用于将表达式的值赋值给变量

?

#include <iostream>
using namespace std;

int main()
{
	//赋值运算符

	// =
	int a = 10;
	a = 100;
	cout << "a = " << a << endl;

	// +=
	a = 10;
	a += 10;
	cout << "a = " << a << endl;

	// -=
	a = 10;
	a -= 10;
	cout << "a = " << a << endl;

	// *=
	a = 10;
	a *= 10;
	cout << "a =" << a << endl;

	// /=
	a = 10;
	a /= 10;
	cout << "a = " << a << endl;

	// %=
	a = 10;
	a %= 10;
	cout << "a = " << a << endl;

	system("pause");
	return 0;
}

3.3 比较运算符

#include <iostream>
using namespace std;

int main()
{
	//比较运算符
	//==
	int a = 10;
	int b = 20;
	cout << (a == b)<< endl;
	
	//!=
	cout << (a != b) << endl;
	
	//>
	cout << (a > b) << endl;
	
	//<
	cout << (a < b) << endl;
	
	//>=
	cout << (a >= b) << endl;

	//<=
	cout << (a <= b) << endl;
	system("pause");
	return 0;
}

3.4 逻辑运算符

作用：用于根据表达式的值返回真值或者假值

?

#include <iostream>
using namespace std;

int main()
{
	//逻辑运算符  非  ！
	int a = 10;
	//在c++中，除了0都为真
	cout << !a << endl;

	cout << !!a << endl;

	system("pause");
	return 0;
}

#include <iostream>
using namespace std;

int main()
{
	//逻辑与&&：两个条件都为真，结果才为真
	int a = 10;
	int b = 10;

	cout << (a && b) << endl;

	a = 0;
	b = 10;
	cout << (a && b) << endl;

	a = 0;
	b = 0;
	cout << (a && b) << endl;
	//同真为真，其余为假

	system("pause");
	return 0;
}

#include <iostream>
using namespace std;

int main()
{
	//逻辑或||：如果两个中有一个为真，结果为真，全为假，结果才为假

	int a = 10;
	int b = 10;

	cout << (a || b) << endl;

	a = 0;
	b = 10;

	cout << (a || b) << endl;

	a = 0;
	b = 0;

	cout << (a || b) << endl;

	//逻辑或，同假为假，其余为真

	system("pause");
	return 0;
}

4. 程序流程结构

?4.1 选择结构

4.1.1 if语句

1. 单行格式if语句

2.多行格式if语句

3.多条件if语句

#include <iostream>
using namespace std;

int main()
{
	//选择结构 
	//用户输入分数，如果分数大于600，视为考上一本大学，在屏幕上输出

	//1.用户输入分数

	//2.打印用户输入的分数

	//3.判断分数是否大于100，如果大于，考上一本，否则，没考上一本

	int score;
	cout << "请输入考试分数：" << endl;
	cin >> score;
	cout << "考试分数为：" << score << endl;

	if (score > 600)
	{
		cout << "恭喜您考上一本大学" << endl;
	}
	else {
		cout << "很遗憾您没考上一本大学" << endl;
	}
	system("pause");
	return 0;
}