Why this code will cause an error

Question

#include<iostream>
using namespace std;
int main()
{
int a=09;
cout<<a;
}
https://code.sololearn.com/cI4FL3C0Hvv4/?ref=app

Answer 1

Because 09 is an invalid octal number,
When add zero in front of a number the compiler looks that number as an octal number,
And an octal number ranges between 0-7 digits

Answer 2

Мг. Кнап🌠 thanks bro

Answer 3

I change 012 to 0123 and now it is giving output 83?

Because, it's taken as octal base (8), since that numeral have 0 in leading. So, it's corresponding decimal value is 10.

012 :
(2 * 8 ^ 0) + (1 * 8 ^ 1) = 10
0123 :

(3 * 8 ^ 0) + (2 * 8 ^ 1) + (1 * 8 ^ 2) = 83

Answer 4

Now i understand that 0 is for octal