The formal name for
~ is tilde.
Many programmers call it twiddle.
A slash or forward slash is
/. If north is at the top of the page, it points southwest-to-northeast. It is tilted the same way that most right-handed people slant their writing, so it has a "forward" slant. Standard American keyboards have
A whack or backslash is
\. If north is at the top of the page, it points northwest-to-southeast. Standard American keyboards have
See also "What do programmers call these punctuation marks? (Parentheses, brackets, ticks, etc.)"
The ASCII entry in The New Hacker's Dictionary, as edited by Eric S. Raymond, includes English-language computer programming names for many common symbols.