C++格式化输出

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

using namespace std;

int main()
{
    
//    boolalpha 可以让 bool 值按字符串输出 
    cout<<"before operating: "<<true<<boolalpha<<endl;
    cout<<"after operating: "<<true<<noboolalpha<<endl;
    
//    showbase 显示进制，uppercase 在十六进制打印 0x、在科学记数法打印 e
//    oct 打印八进制，hex 打印十六进制，dec 打印十进制 ，也可以用 setbase(base) 来设置进制 
    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; 

//    我们可以使用 cout.precision(size) 或 setprecision(size) 来设置精度
//    即几位数字，通过 cout.precision() 返回当前精度值 
    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 对浮点值总是显示小数点，showpos 对非负数显示 +  
    cout<<"before operating the num is: "<<2.0<<endl;
    cout<<showpoint<<showpos<<"after operating: "<<2.0<<noshowpoint<<noshowpos<<endl;
    
//    sciencetific 用科学计数法显示浮点数，acos 为反三角函数，在头文件 cmath 里 
    cout<<scientific<<"scientific: "<<acos(-1)<<endl;
    
//    setw(width) 设置宽度为 width 个字符，right 为右对齐，left 为左对齐，setfill(ch) 用 ch 来填充 
    cout<<setw(20)<<setfill('*')<<left<<"i love u"<<endl<<setw(20)<<right<<"i love u too";
    cout<<endl; 
    
//    unitbuf 每次输出操作都刷新缓冲区，对应nounitbuf；skipws 输入运算符跳过空白符，对应 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;
}