cout(打印)
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.. code-block:: c++
    :caption: cout 示例代码
    
    //打印字符串
    cout<<"Hello World!";

    //打印变量
    cout<<a;

    //打印多条内容
    cout<<"one"<<"two"<<a;

    //打印完换行
    //方法一：
    cout<<"line 1."<<endl;
    //方法二：
    cout<<"line 2."<<"\n";
    //方法三：
    cout<<"line 3.\n";