-D name=definition and bitwise operator

I am trying to understand how the next calculation is performed.

For example, if this is my terminal command

gcc ex2.c -D b+=2

Why do I get 5?

#include <stdio.h>

int main() 
{
#ifdef b
    printf("%d\n", 2 b | ~ 2 b);
#endif
    return 0;
}

2 b mean 2*b ?

~ 2 b mean 2*b and then ~ ?

compiling with gcc ex2.c -D b+=2 define b as +2 so the source

#include <stdio.h>

int main() 
{
#ifdef b
    printf("%d\n", 2 b | ~ 2 b);
#endif
    return 0;
}

is like

#include <stdio.h>

int main()
{

    printf("%d\n", 2 + 2 | ~ 2 + 2);

    return 0;
}

and for me that prints -1

to see the result after the preprocessing use the option -E :

/tmp % gcc ex2.c -E -D b+=2
<command-line>: warning: missing whitespace after the macro name
...
# 2 "ex2.c" 2

int main()
{

    printf("%d\n", 2 + 2 | ~ 2 + 2);

    return 0;
}