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# How C++ identify the base of a number?

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This article is regarding How C++ identify the base of a number? Integer Literals in C++.
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◕ What is Integer Literals in C++?
In other word we can say integer literal is a constant number, such as 1, 2, 5, 100, 105 etc.

◕ C++ allows us to write integers in three different number bases:

1. Base 10 ( Decimal )
2. Base 8 ( Octal )
3. Base 16 ( Hexadecimal)

◕ How C++ identify the Base of a Number?

- C++ uses the first one digit or first two digits to identify the base of a number.

- If the first digit is in the range 1–9, then the base of the number is 10 i.e. it is a Decimal Number.
Example: 45 is a Decimal Number and its base is 10.

- If the first digit is 0 and the second digit is in the range 1–7, then the base of a number is 8 i.e. it is an Octal Number.
Example: 012 is an Octal Number and it's base is 8.

- If the first two digits are 0x ( Zero & x ) or 0X, then the base of the number is 16 i.e it is a Hexadecimal Number.
Example: 0x12 is a Hexadecimal Number and it's base is 16.

◕ By default, in C++, cout displays integers in Decimal form, regardless of how they are written in a program. This means, if we write a program in Octal or in Hexadecimal form then the output will show in Decimal by-default.

The example is given bellow.

Let we have a program like this:

#include <iostream>
using namespace std;
int main(){
int wing = 999; // this is in Decimal form
int bird = 025; // this is in Octal form
int tree = 0X55; // this is in Hexadecimal form
cout << "Decimal value of 'wing' " << wing << endl;
cout << "By-default Octal value will show in Decimal. Here it is: " << bird << endl;
cout << "By-default Hexadecimal value will show in Decimal. Here it is: " << tree << endl;
return 0;
}

The output is:
Decimal value of 'wing' 999
By-default Octal value will show in Decimal. Here it is: 21
By-default Hexadecimal value will show in Decimal. Here it is: 85

Related article:
How to display a value in Hexadecimal form in C++?
How to display a value in Octal form in C++?
How C++ identify the base of a number?

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