Toggle between c/h-files

.vimrc

function! ToggleCH()
    let extension = expand('%:e')

    if extension =~ 'c'
        let extension = '.h'
    elseif extension =~ 'h'
        let extension = '.c'
    else
        return
    endif

    let filename = expand('%:r') . extension

    if filereadable(filename)
        execute "e " . filename
    endif
endfunction
command! -register ToggleCH call ToggleCH()
nnoremap <silent> <leader>h :<C-u>ToggleCH<CR>