function xx = fsk_gen( bitstr, fs, bdur)

len_bitstr = length(bitstr);

num_array = abs(bitstr);

bin_string = DEC2BIN(num_array,8);

len_binstr = length(bin_string);

k = len_binstr * len_bitstr;

reshape(bin_string,1,k);

inbits = abs(bin_string) - abs('0'); % convert string to array of
binary numbers

xx = [];

tvec = [0:fs*bdur]/fs; % determine time interval

%% Determine the frequency to output from the array of binary numbers

for i = 1:length(inbits)
    
    
    if (inbits(i) == 1)
        xxp = 1650;
    elseif (inbits(i) == 0)
        xxp = 1850;
    else
        'error'
    end
    
    xx = [xx zeros(1,fs/50000)]; %<- this is line 43
    xx = [xx cos(2*pi*xxp*tvec)];
end

specgram(xx,[],fs)
soundsc(xx,9000)

This function is running EXACTLY as i wish it to; however i am
getting the following message: Warning: Size vector should be a row
vector with integer elements.
> In fsk_gen at 43

Any ideas? thanks!