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>
using namespace std;
int main(){
    int a = 10;
    int b = 3;
    double c = 3;
    cout << "a + b = "<< a + b << endl;
    cout << "a - b = "<< a - b << endl;
    cout << "a x 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;
//    cout << "a % c = "<< a % c << endl; // 小数不能取模

}

#include <iostream>
using namespace std;
int main(){
    int a = 10;

    // 共同点 都是自增一次
//    a++;
//    cout<<a<< endl;  //11
//    ++a;
//    cout <<a <<endl;  //12

    // 不同:
    // 前置++是先自增,再参与运算
    // 后置++是先参与运算,再自增
    int b = 3;
    int c = a++*3 + b;
    cout << c <<endl;  //33
    int d = ++a*3 + b;
    cout << d <<endl;  //39
    cout << a++ <<endl;  // 12
    cout << ++a <<endl;  // 14
}

赋值运算符

image

#include <iostream>
using namespace std;
int main(){
    int  age = 18;
//    age = age + 20;
    age += 20;
    cout <<age<< endl;
    int b = 10;
    b*=3;
    cout <<b<< endl;
}

比较运算符

image

#include <iostream>
using namespace std;
int main(){
//    int a = 10;
//    int b = 10;
    int a;
    int b;
    cout << "please input a "<<endl;
    cin >>a;
    cout << "please input b "<<endl;  
    cin >>b;
    cout << "a == b  "<< (a==b) <<endl;  // 1 true
    cout << "a != b  "<< (a!=b) <<endl;  // 0 fasle
    cout << "a <= b "<< (a<=b) <<endl;
    cout << "a < b "<< (a<b) <<endl;
    cout << "a >= b "<< (a>=b) <<endl;
    cout << "a > b " << (a>b) <<endl;
}

逻辑运算符

#include <iostream>
using namespace std;
int main(){
    int a = 10;

    // 非
    bool res1 = !a;
    cout <<res1 <<endl;
    cout <<!!a <<endl;

    // 与  同真为真
    int b = 11;
    int c = 12;
    cout << (a < b && a < c) <<endl; // 1
    cout << (a > b && a < c) <<endl; // 0

    // 或  有一个为真就是真
    cout << (a < b || a < c) <<endl; // 1
    cout << (a > b || a < c) <<endl; // 1
    cout << (a > b || a > c) <<endl; // 0
    
}

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
}

#include <iostream>
using namespace std;
int main(){
    int age;
    cout << "please input your age"<<endl;
    cin >> age;
    if (age >= 18){
        cout << "cheng nian"<<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;
int main(){
    int age;
    cout << "please input your age"<<endl;
    cin >> age;
    if (age >= 18){
        cout << "cheng nian"<<endl;
    }else{
        cout << "bao bao "<<endl;
    }
}

多重判断

#include <iostream>
using namespace std;
int main(){
    int score;
    cout << "please input your score"<<endl;
    cin >> score;
    // if  else if  else 下面只有一行语句的时候可以省略大括号
    if (score >= 90 && score <= 100)
        cout << "A level"<<endl;
    else if (score >= 75 && score < 90)
        cout << "B level"<<endl;
    else if (score >= 60 && score < 75)
        cout << "C level"<<endl;
    else if (score >= 0 && score < 65)
        cout << "D level"<<endl;
    else
        cout << "data error"<<endl;

}

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？

image

#include <iostream>
using namespace std;
int main(){
    double pigA;
    cout << "please input pigA weight"<<endl;
    cin >> pigA;
    double pigB;
    cout << "please input pigB weight"<<endl;
    cin >> pigB;
    double pigC;
    cout << "please input pigC weight"<<endl;
    cin >> pigC;
    double maxWeight;
//    if (pigA > pigB)
//        maxWeight = pigA;
//    else
//        maxWeight = pigB;
//    if (maxWeight < pigC)
//        maxWeight = pigC;
//    cout << "the most weighted"<<maxWeight<<endl;

    if (pigA > pigB){
        if (pigA > pigC){
            cout << "pigA = "<<pigA<<endl;
        } else{
            cout << "pigC = "<<pigC<<endl;
        }
    } else{
        if (pigB > pigC){
            cout << "pigB = "<<pigB<<endl;
        } else{
            cout << "pigC = "<<pigC<<endl;
        }
    }

}

BMI计算器

image

计算公式为：BMI=体重÷身高^2。（体重单位：千克；身高单位：米。）

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