科学计数法

# include <iostream>
using namespace  std;
int main () {
    // 科学计数法
    float a = 1e5; // 10^5
    cout << a << endl;
    float b = -4e3;  // -4 x 10^3
    cout << b << endl;
    double c = 4e-2; // 0.04
    cout << c << endl;

    double d = 4e-5; // 0.00004
    cout << d << endl;



}

字符型 (char型)

作用: 字符型变量⽤于显⽰单个字符

• C和C++中字符型变量只占⽤1个字节
• 字符型变量并不是把字符本⾝放到内存中存储，⽽是将对应的ASCII编码放⼊到存储单元

# include <iostream>
using namespace  std;
int main () {
    // 科学计数法
    float a = 1e5; // 10^5
    cout << a << endl;
    float b = -4e3;  // -4 x 10^3
    cout << b << endl;
    double c = 4e-2; // 0.04
    cout << c << endl;

    double d = 4e-5; // 0.00004
    cout << d << endl;
}

ASCII 码⼤致由以下两部分组成：

• ASCII ⾮打印控制字符： ASCII 表上的数字 0-31 分配给了控制字符，⽤于控制像打印机等⼀些外围 设备。
  ASCII 打印字符：数字 32-126 分配给了能在键盘上找到的字符，当查看或打印⽂档时就会出现。

字符串型

作⽤：⽤于表⽰⼀串字符
两种风格

• C风格字符串 : char 变量名[] = "字符串值"

# include <iostream>
using namespace  std;
int main () {
    char str[] = "hello world";
    cout << str<< endl;
}

• C++风格字符串 : string 变量名 = "字符串值"

# include <iostream>
# include <string>
using namespace  std;
int main () {
    // c++
    string string1 = "hello world";
    cout << string1<< endl;
}

c++风格字符串需要引入头文件#include <string>

布尔数据类型 boolean

布尔数据类型代表真或假的值
bool类型只有两个值：

• true --- 真（本质是1）
• false --- 假（本质是0）
  bool类型占1个字节⼤⼩

# include <iostream>
# include <string>
using namespace  std;
int main () {
    // 整型输入
    int age;
    cout << "please input your age" << endl;
    cin>>age; // 将console中的数据赋给变量a
    cout << "age = " << age << endl;
    // 浮点型输入
    double height;
    cout << "please input your height" << endl;
    cin>>height; // 将console中的数据赋给变量age
    cout << "height = " << height << endl;
    // 字符型输入
    char ch;
    cout << "please input a char" << endl;
    cin>>ch;
    cout << "ch = " << ch << endl;

    // 字符串型输入
    string name;
    cout << "please input your name" << endl;
    cin>>name;
    cout << "name = " << name << endl;

    // 布尔型输入
    bool flag;
    cout << "please input a flag" << endl;
    cin>>flag; 
    cout << "flag = " << flag << endl;
}

运算符

算术运算符： 四则运算
赋值运算符： 将表达式的值赋给变量
比较运算符： 表达式的比较， 返回布尔值
逻辑运算符： 根据表达式的值返回真或者假

算术运算符

# include <iostream>
# include <string>
using namespace  std;
int main () {

    int a =  10;
    int b =  3;
    double c =  3.0;
    cout << "a + b = " << a + b << endl;
    cout << "a - b = " << a - b << endl;
    cout << "a * b = " << a * b << endl;
    cout << "a / b = " << a / b << endl;  // 整除
    cout << "a / c = " << a / c << endl;  // 整除
    cout << "a % b = " << a % b << endl;
}

++前置和后置区别

# include <iostream>
using namespace  std;
int main () {
    // 参与运算的时候会有区别
    int a = 10;
    // 前置++ 先自增, 然后参与运算
//    int b = ++a*10;
//    cout << "b = " << b << endl;

    // 后置++ 先参与运算, 然后自增
    int b = a++*10;
    cout << "b = " << b << endl;
    cout << "a = " << a << endl;

    int  c = 100;

    cout << "c = " << ++c << endl; // 101
    cout << "c = " << c++ << endl; // 101
}

赋值运算符

# include <iostream>
using namespace  std;
int main () {

    int age = 10;
//    age = age + 20;
    age += 20;
    cout << age <<endl;

}

比较运算符

# include <iostream>
using namespace  std;
int main () {

    int a = 10;
    int b = 20;
    cout << (a == b) << endl; // 0 false
    cout << (a > b) << endl; // 0 false
    cout << (a >= b) << endl; // 0 false
    cout << (a != b) << endl; // 1 true
    cout << (a < b) << endl; // 1 true
    cout << (a <= b) << endl; // 1 true
   
}