function fahrenheitEntry
global tempConvState; 

s = get(tempConvState.f, 'String');
ftemp = str2num(s); %! convert to a number
if isempty(ftemp) %! conversion unsuccessful
    cstr = '';
    mstr = 'Invalid Fahr entry';
else
    cstr = num2str( 5*(ftemp-32)/9 );
    mstr = '';
end
set(tempConvState.c, 'String', cstr); %! update the display
set(tempConvState.m, 'String', mstr);