stay C++ In the integer constant of , Integers are divided into decimal integers 、 Octal and hexadecimal integers .

Given an integer constant, how to distinguish which system is it ？/ Give an integer constant , Such as 100, The default is decimal , If you add before the number 0, Such as 0100, Then this number is expressed as an octal number , If you add before the number 0x, Such as 0x100, Then this number is expressed as a hexadecimal number .

Use cout When you output an integer , By default, the output is in decimal system , If you want the number to be output in octal or hexadecimal , You need to use the output format controller ./ If you use format controllers , To include header files iomanip.
The decimal output format controller is dec（ By default ）, Octal format control is oct, The hexadecimal format controller is hex.

Here is an example of the program

```// The use of different base integers
// Give an integer constant , Such as 100, The default is decimal ,
// If you add before the number 0, Such as 0100, Then this number is expressed as an octal number
// If you add before the number 0x, Such as 0x100, Then this number is expressed as a hexadecimal number
// Use cout When you output an integer , By default, the output is in decimal system ,
// If you want the number to be output in octal or hexadecimal , You need to use the output format controller
// If you use format controllers , To include header files iomanip
// The decimal output format controller is dec, Octal format control is oct, The hexadecimal format controller is hex
#include <iostream>
#include <iomanip> // Contains the output format control header file
using namespace std;
int main()
{
cout<<" The following integers are output in decimal system "<<endl;
int a; // integer a
a=; // Assign a decimal integer value to
cout<<"after a=11( Decimal system 11), a="<<a<<"( Decimal system )"<<endl;
a=; // Assign an octal integer value to
cout<<"after a=011( octal 11), a="<<a<<"( Decimal system )"<<endl;
a=0x11; // Assign an octal integer value to
cout<<"after a=0x11( Hexadecimal 11), a="<<a<<"( Decimal system )"<<endl<<endl;
cout<<" The following integers are output in the decimal system specified by the output format controller "<<endl;
a=; // Assign a decimal integer value to
cout<<"after a=11( Decimal system 11), a="<<dec<<a<<"( Decimal system )"<<endl;
a=; // Assign an octal integer value to
cout<<"after a=011( octal 11), a="<<oct<<a<<"( octal )"<<endl;
a=0x11; // Assign an octal integer value to
cout<<"after a=0x11( Hexadecimal 11), a="<<hex<<a<<"( Hexadecimal )"<<endl;
return ;
}```

Running results

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