how to add 2 or more different length signals?

I want to add 2 or more signals to play them at the same time, like a sampler. If i know well i need to convert them to the same sampling rate. How can i do that if i have a big sample library? If sample A is longer than sample B, after B finishes playing, the rest from A should continue playing till end. So it's only need a simple addition from the beginning of each other until the longest sample finishes?

Thx in advance

I tried with this source code:

clear;

clc;

myFolder = 'C:\Users\Aron\Samples\proba';

if exist(myFolder, 'dir') ~= 7

Message = sprintf('Error: The following folder does not exist:\n%s', myFolder);

uiwait(warndlg(Message));

return;

end

filePattern = fullfile(myFolder, '*.wav');

wavFiles = dir(filePattern);

sampleArray = cell(length(wavFiles),1);

Fs = zeros(size(sampleArray));

 for k = 1:length(wavFiles)

    baseFileName = wavFiles(k).name;

    fullFileName = fullfile(myFolder, baseFileName); 

    fprintf(1, 'Now reading %s\n', fullFileName);   

    [sampleArray{k}, Fs(k)] = wavread(fullFileName);

 end

s=1;

data_1=(sampleArray{s});

%sound(data_1);

%%

L = length(data_1);

NFFT = 2^nextpow2(L); % Next power of 2 from length of y

Y = fft(data_1,NFFT)/L;

f = Fs/2*linspace(0,1,NFFT/2+1);

% Plot single-sided amplitude spectrum.

figure(1);

plot(f,2*abs(Y(1:NFFT/2+1)))

title('Single-Sided Amplitude Spectrum of y(t)')

xlabel('Frequency (Hz)')

ylabel('|Y(f)|')

%%

g=9;

data_2=(sampleArray{g});

L = length(data_2);

NFFT = 2^nextpow2(L); % Next power of 2 from length of y

X = fft(data_2,NFFT)/L;

f = Fs/2*linspace(0,1,NFFT/2+1);

data_sum=Y+X;

data_sum_in_time = ifft(data_sum,NFFT)*L;

sound (data_sum_in_time);