C++格式化輸出

#include <iostream>
#include <iomanip>
#include <cmath> 

using namespace std;

int main()
{
    
//    boolalpha 可以讓 bool 值按字符串輸出 
    cout<<"Before operating: "<<true<<boolalpha<<endl;
    cout<<"After operating: "<<true<<noboolalpha<<endl;
    
//    showbase 顯示進制，uppercase 在十六進制打印 0X、在科學記數法打印 E
//    oct 打印八進制，hex 打印十六進制，dec 打印十進制 ，也可以用 setbase(base) 來設置進制 
    int num = 0;    cout<<"Enter the num: ";    cin>>num;
    cout<<showbase<<uppercase<<"Default: "<<num<<endl;
    cout<<"Octal: "<<oct<<num<<endl;
    cout<<"Hex: "<<hex<<num<<endl;
    cout<<"Decimal: "<<dec<<num<<noshowbase<<nouppercase<<endl; 

//    我們可以使用 cout.precision(size) 或 setprecision(size) 來設置精度
//    即幾位數字，通過 cout.precision() 返回當前精度值 
    cout<<"Precision: "<<cout.precision()<<", Value: "<<sqrt(2.0)<<endl;
    cout.precision(12);
    cout<<"Precision: "<<cout.precision()<<", Value: "<<sqrt(2.0)<<endl;
    
    cout<<setprecision(3);
    cout<<"Precision: "<<cout.precision()<<", Value: "<<sqrt(2.0)<<endl;
    
//    showpoint 對浮點值總是顯示小數點，showpos 對非負數顯示 +  
    cout<<"Before operating the num is: "<<2.0<<endl;
    cout<<showpoint<<showpos<<"After operating: "<<2.0<<noshowpoint<<noshowpos<<endl;
    
//    sciencetific 用科學計數法顯示浮點數，acos 為反三角函數，在頭文件 cmath 里 
    cout<<scientific<<"Scientific: "<<acos(-1)<<endl;
    
//    setw(width) 設置寬度為 width 個字符，right 為右對齊，left 為左對齊，setfill(ch) 用 ch 來填充 
    cout<<setw(20)<<setfill('*')<<left<<"I LOVE U"<<endl<<setw(20)<<right<<"I LOVE U TOO";
    cout<<endl; 
    
//    unitbuf 每次輸出操作都刷新緩沖區，對應nounitbuf；skipws 輸入運算符跳過空白符，對應 noskip
    cout<<unitbuf;    cin>>noskipws;
    cout<<"Enter the chars or enter the '!' to end it: "<<endl;
    char ch;
    while (cin>>ch && ch != '!')
        cout<<ch;
    cout<<nounitbuf;    cin>>skipws;
    
    system("pause");
        
    return 0;
}