Why is the & 1 and + '0' is needed to display the binary number?

Question

I got this code here to print the binary of a decimal, if I ran this function with argument as 3, it would print 0000 0011, which is right, I understand that >> will shift the binary to the right 7 to 0 to display the binary, but I do not understand the purpose of the code: & 1 and + 0, can someone tell me what are those for?

void gal_print(gal8 a)
{
    int i = 8;
    while (i--)
       // printf("%d", i);
        putchar((a >> i & 1) + '0');
}

Answer 1

This expression with the bitwise operator & (bitwise AND operator)

a >> i & 1

is used to extract the right most bit of the number. So the result value of the expression will be either 0 or 1.

For example

00000011 // 3
&
00000001 // 1
========
00000001 // 1

or

00000010 // 2
&
00000001 // 1
========
00000000 // 0

As there is used the function putchar then this integer value is required to be converted to character.

putchar((a >> i & 1) + '0');

That is '0' + 0 gives the character '0' and '0' + 1 gives the character '1'.