Why zero at the beginning of int variable gives error?

[Sohail Ahmed]

#include <iostream>
using namespace std;
int main()
{
    struct information
    {
        string  name;
        string  bloodgroup;
        int     mobno;
    };
 
    information person1={"Ali Hamza","O-",434233434};
    information person2={"Akram Ali","B",034};
    cout << endl << person1.name << endl;
    cout << person1.bloodgroup << endl << person1.mobno<< endl;
    cout << endl << person2.name << endl << person2.bloodgroup << endl << person2.mobno<<endl;
 
    int bh = 09;
    cout << bh;
 
    return 0;
}

I wonder when I saw errors like invalid digit in octal constant 9 and 8.Also it print wrong value for the value of "mobno"(in structure) if zero is the first digit, but it give error when zero is used as first digit for num at the end of program.Is there someone who would explain it for me?

[computerfox]

I would suggest changing mobno to a string. Does the assignment require it to be an integer?
Usually contact information, including mobile numbers, are taken as strings.

[Rabbit]

The reason is that numbers starting with a 0 is how you define an octal, base 8 number. Numeric data types can't store leading zeroes.