What is &= and |=

Question

I was going through some VC++ code in a large code-base and came across this:

    if (nState & TOOL_TIPS_VISIBLE)
        nState &= ~TOOL_TIPS_VISI         


        

Answer 1

x &= y;

is equivalent to:

x = x & y;

In the same way,

x|= y;

is equivalent to:

x = x | y;