if exists("*<SID>CAltSwitcher") | finish | endif

let g:AltExts = {
    \ "c": ["h"],
    \ "h": ["c", "cc"],
    \ "cc": ["hh", "h"],
    \ "hh": ["cc"]
\}

function! <SID>CAltSwitcher() abort
    for ext in g:AltExts[expand("%:e")]
        let name = expand("%<") . "." . ext
        if filereadable(name)
            execute "edit " . name
            return
        endif
    endfor
    echomsg "no alt found"
endfunction

nnoremap <buffer> <C-^> :call <SID>CAltSwitcher()<CR>