从熟练Python到入门学习C++（record 3）

运算符

1.算数运算符

注意点：

1.整数相除，还是整型，负责为实型；

2.前置和后置的区别，赋值规则不同；

3.除和模的分母不能为0；

4.小数不能取余；

#include <iostream>
using namespace std;

int main()
{
    int a = 8;
    int b = 3;
    float c = 3.0f;
    cout << a + b << endl;
    cout << a/b << " VS " << a/c << endl;
    ++a;
    cout << "a : " << a << endl; 
    a++;
    cout << "a : " << a; 
    return 0;
}

2.赋值运算符

3.比较运算符

注意：在cout时候，需要加括号

#include <iostream>
using namespace std;

int main()
{
    int a = 10; int b = 20; int c = 10;
    cout << (a == b) << endl;
    bool d = a==c;
    cout << d << endl;
    return 0;
}

4.逻辑运算符

（&&，||）相当于python的（and，or)。对于！，记住非0都是真。

程序流程符号

5.选择结构

if语句，比python的if多括号，更加完整。因为python的每一行的缩进都是固定的，而c++不需要缩进。

#include <iostream>
using namespace std;

int main()
{
    int a;
    cin >> a;
    if (a > 90)
    {
        cout << "score is enough\n";
    }
    else if ( a > 80)
    {
        cout << "score is danger\n";
    }
    else
    {
        cout << "score is bad\n";
    }
    return 0;
}

三目运算符

相当于python的：表达式2 if 表达式1 else 表达式3

注意：要加括号才能赋值

#include <iostream>
using namespace std;

int main()
{
    int a = 10;
    int b = 20;
    int c = 30;
    int d = a ? b : c;
    cout << "d : "  << d << endl; // d : 20
    // 三目运算符也能赋值
    (a>b ? b : c) = 100;
    cout << "a : " << a << endl; // a : 10
    cout << "b : " << b << endl; // b : 
    cout << "c : " << c << endl; // c : 
    return 0;
}

switch语句

#include <iostream>
using namespace std;

int main()
{
    int x = 10;
    switch (x)
    {
        case 10:
            cout << "10\n";
            break;
        case 9:
            cout << "9\n";
            break;
        default:
            cout << "no\n";
            break;
        
    }
    return 0;
}

6.循环结构

6.1while语句

与python一模一样

#include <iostream>
#include <ctime>
using namespace std;

int main()
{
    srand(time(0));
    int x = rand() % 100 + 1; // 1-100
    int y;
    cin >> y;
    while (x != y)
    {
        if (y > x)
        {
            cout << "bigger\n";
        }
        else
        {
            cout << "smaller\n";
        }
        cin >> y;
    } 
    cout << "sucess\n";
    return 0;
}

6.2do while语句

 先进行，再判断；发现一个规律，大括号中写程序，圆括号中写判断。

#include <iostream>
#include <math.h>
using namespace std;

int main()
{
    int x = 100;
    int y = 0;
    cout << "start" << endl;
    do
    {
        int x1,x2,x3;
        x1 = pow(x / 100, 3);
        x2 = pow(x % 100 / 10, 3);
        x3 = pow(x % 10, 3);
        if (x1+x2+x3 == x)
        {
            ++y;
            cout << x1 << " " << x2 << " " << x3 << " : " << x << endl;
        }
        ++x;
    }while (x < 1000);
    cout << "num is " << y << endl;
    return 0;
}

6.3for语句

注意：

1. for的圆括号中，使用；间隔

2. 流程是从起始表达式开始，条件成立后运行语句，再经过末尾循环体，重复判断条件表达式。

#include <iostream>
#include <math.h>
using namespace std;

int main()
{
    for (int i = 1; i < 101; i++)
    {
        int x1,x2;
        x1 = i % 10;
        x2 = i / 10;
        if (x1 == 7 || x2 == 7 || i % 7 == 0)
        {
            cout << i << endl;
        }
    }
    return 0;
}

6.4嵌套循环

冷饭新炒；

#include <iostream>
using namespace std;

int main()
{
    for (int i = 1; i < 11; i++ )
    {
        for (int i = 1; i < 11; i++ )
        {
            cout << "* ";
        }
        cout << "\n";
    }

    for (int i = 1; i <= 9; i++)
    {
        for (int j = 1; j <= i; j++)
        {
            cout << j << " * " << i << " = " << i*j << " | ";
        }
        cout << "\n";
    }
    return 0;
}

7.break，continue，以及goto

break和continue与python中的函数一样

goto

#include <iostream>
using namespace std;

int main()
{
    cout << "1" << endl;
    goto FLAG;

    for (int i = 1; i < 10; i++)
    {
        cout << i << endl;
    }
    FLAG:

    cout << "2" << endl;
}