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

#include <iostream>
using namespace std;
// 运算符示例
int main() {
    int a1 = 10;
    int b1 = 3;

    cout<< a1 + b1 << endl;
    cout<< a1 - b1 << endl;
    cout<< a1 * b1 << endl;
    cout<< a1 / b1 << endl; // 两个整数相除整除结果依然是整数
    // 除数不能为 0
//    b1 = 0;
//    cout<<" a1 / b1 = "<< a1 / b1 << endl; // 会有错误

    int a2 = 10;
    int b2 = 20;
    cout<< a2 / b2 << endl; // 0
    // 小数相除
    double d1 = 0.5;
    double d2 = 0.25;
    double res = d1/d2;
    cout<<"d1/d2 = " <<res<< endl;
}

取模

#include <iostream>
using namespace std;
// 运算符示例  取模
int main() {
    int a1 = 10;
    int b1 = 3;
    cout<< a1 % b1 << endl; // 1
    // 除数不能为 0
//    b1 = 0;
//    cout<<" a1 / b1 = "<< a1 / b1 << endl; // 会有错误
    // 取模除数也不能为0
    int a2 = 10;
    int b2 = 20;
    cout<< a2 % b2 << endl; // 10
    // 小数不能取模
//    double d1 = 0.5;
//    double d2 = 0.25;
//    double res = d1%d2;
//    cout<<"d1/d2 = " <<res<< endl;
}

自增运算

#include <iostream>
using namespace std;
// 自增运算符
int main() {
    // 后置递增
    int a = 10;
    a++; // 等价于 a = a + 1
    cout << "a = " << a << endl;
    // 前置递增
    int b = 10;
    ++b; //
    cout << "b = " << b << endl;
    //  区别
    // 前置递增是先对变量进行++， 然后再参与计算表达式
    int a2 = 10;
    int b2 = ++a2*10;
    cout << "b2 = " << b2 << endl;
    cout << "a2 = " << a2 << endl;

    // 后置递增是先参与计算表达式， 然后再对变量进行++
    int a3 = 10;
    int b3 = a3++*10;
    cout << "b3 = " << b3 << endl;
    cout << "a3 = " << a3 << endl;

}

赋值运算符

#include <iostream>

using namespace std;

// 赋值运算符
int main() {
    //
    int a = 10;
    cout << "a = " << a << endl;
    a = 100;
    a += 2; // a = a + 2
    cout << "a = " << a << endl;
    a -= 2;
    cout << "a = " << a << endl;
    a *= 2;
    cout << "a = " << a << endl;
    a /= 2;
    cout << "a = " << a << endl;
    a %= 2;
    cout << "a = " << a << endl;
}

比较运算符

#include <iostream>
using namespace std;
// 比较运算符
int main() {
    int a = 10;
    int b = 20;
    cout <<(a == b) << endl; // 0 false
    cout <<(a != b) << endl; // 1 true
    cout <<(a > b) << endl; // 0 false
    cout <<(a < b) << endl; // 1 true
    cout <<(a <= b) << endl; // 1 true
    cout <<(a >= b) << endl; // 0 false
    int res = (a == b);
    cout <<"res = "<< res << endl; // 0 false
    bool flag = (a == b);
    cout <<"flag = "<< flag << endl; // flag = 0
    //    在c++/c 中比较运算 真 用 1 表示 假用 0 表示

}

逻辑运算符

#include <iostream>

using namespace std;

// 逻辑运算符
int main() {
    // 非
    int a = 100;
    cout << !a << endl; // 0
    cout << !!a << endl; // 1
    // 与
    int b = 10;
    int c = 10;
    cout << (b && c) << endl; // 1
    // 或
    int d = 0;
    cout << (d || c) << endl; // 1

}

image.png

程序流程结构

C/C++⽀持最基本的三种程序运⾏结构：顺序结构、选择结构、循环结构

顺序结构：程序按顺序执⾏，不发⽣跳转
选择结构：依据条件是否满⾜，有选择的执⾏相应功能
循环结构：依据条件是否满⾜，循环多次执⾏某段代码
选择结构

单行if
if(条件){
 条件为真时执行的事情
}

栗子1

#include <iostream>
using namespace std;
// 选择结构
int main() {
    int score;
    cout<< "please input your score"<< endl;
    cin >> score;
    cout<< "your score is "<< score<< endl;
    if (score >= 600){
        cout<< "your score is very good "<< endl;
    }
}

if(条件){
 条件为真时执行的事情
}else{
 不满足条件为真时执行的事情
}

#include <iostream>
using namespace std;
// 成绩level显示器
int main() {
    int score;
    cout<< "please input your score"<< endl;
    cin >> score;
    cout<< "your score is "<< score<< endl;
    if (score >= 90 && score <= 100){
        cout<< "your score level is A "<< endl;
    }else if (score >= 80 && score < 90){
        cout<< "your score level is B "<< endl;

    }else if (score >= 60 && score < 80){
        cout<< "your score level is C "<< endl;

    }else if (score >= 0 && score < 60){
        cout<< "your score level is D "<< endl;
    }else{
        cout<< "your score is error "<< endl;
    }
}

作业1：三只小猪称重
有三只⼩猪ABC，请分别输⼊三只⼩猪的体重，并且判断哪只⼩猪最重？

#include <iostream>
using namespace std;
int main() {
    int pigA;
    int pigB;
    int pigC;
    cout<< "please input your score"<< endl;
    cin >> pigA;
    cin >> pigB;
    cin >> pigC;
    cout<< "pigA"<<pigA<< endl;
    cout<< "pigB"<<pigB<< endl;
    cout<< "pigC"<<pigC<< endl;


}

作业2：BMI计算器