C++ int with preceding 0 changes entire value

Question

I have this very strange problem where if I declare an int like so

int time = 0110;

and then display it to the console the value returned i

Answer 1

An integer literal that starts from 0 defines an octal integer literal. Now in C++ there are four categories of integer literals

integer-literal:
    decimal-literal integer-suffixopt
    octal-literal integer-suffixopt
    hexadecimal-literal integer-suffixopt
    binary-literal integer-suffixopt

And octal-integer literal is defined the following way

octal-literal:
    0 octal-literal
    opt octal-digit

That is it starts from 0.

Thus this octal integer literal

0110

corresponds to the following decimal number

8^2 + 8^1 

that is equal to 72.

You can be sure that 72 in octal representation is equivalent to 110 by running the following simple program

#include 
#include 

int main() 
{
    std::cout << std::oct << 72 << std::endl;

    return 0;
}

The output is

110