Octal literals in C

When we initialize a value by putting ‘0’ before a number, the number is treated as octal. For instance ’10’ is read as 10 but ‘010’ is read as 8.

Examples:

Input : 0101
Output : 65

Input : 01010
Output : 520

#include<iostream>
using namespace std;
int main()
{
    int x = 0101;
    cout << x;
    return 0;
}

Output:

65

#include<iostream>
using namespace std;
int main()
{
    int x = 020;
    cout << x;
    return 0;
}

Output:

16

#include<iostream>
using namespace std;
int main()
{
    int x = 090;
    cout << x;
    return 0;
}

Output :

Compiler Error : 9 is not a valid digit in octal number.