Please help me with MATLAB code( SOUND FFT Related) analysis.

From if (A == '0') in the code below I did not understand.

Please comment and explain so I'm verry happy~

thank U

clc;
clear all;


%% Parameters 
A = 2;                  % check value from arduino


waveFile = 'test.wav';  % sound file
fs = 44100;             % sampling rate
duration = 2;     % recording time
nbits = 16;             % using 16 bits
ard_1st = 'COM3';
ard_2st = 'COM5';
ard_baud_rate = 9600;


%% 
while 1
    arduino = serial(ard_1st, 'BaudRate', ard_baud_rate);
    fopen(arduino);
    A = fscanf(arduino, '%s');                    % read from 1st arduino
    fclose(arduino);
 
    if (A == '0')                                 % run when arduino sends 0
        fprintf('Recording...\n');
        y = wavrecord(duration*fs, fs);           % recording 
        fprintf('Finished recording.\n');
%         fprintf('Press any key to save the sound data to %s...\n', waveFile); % pause and save manually
        wavwrite(y, fs, nbits, waveFile);         % save into wavefile in sampling rate fs, nbits
        fprintf('Finished writing %s\n', waveFile);
        
        [file, Fs] = wavread('test.wav');         % read wav (amplitude and sampling rate)
        B = size(file(:,1));              
        N = B(1);                             
        f = -1 * (Fs/2) + (Fs/N):(Fs/N):(Fs/2);   % range of frequency
        f_p = 0:(Fs/N):(Fs/2-Fs/N);               % 1/2 of frequeny
        t = 0:1:B-1;                              % time range
        
        f_file = fft(file);                       % do fft
        f_file = abs(f_file);                       
        f_file_shift = fftshift(f_file);          % domain shift
        f_file_shift_p = zeros((N-1)/2,1);         
        
        for i = 1:1:(N/2)
            f_file_shift_p(i,1) = f_file(i,1);
        end                                       % delete f below 0
        
        subplot(2,1,1)
        plot(t,file)                              
        subplot(2,1,2)
        plot(f_p,f_file_shift_p)
        xlim([0 1500])
        ylim([0 3000])
        a = 2;
        
        for j = 100:1:240                         % in 100 ~ 240Hz
            if (f_file_shift_p((N/Fs)*j,1) >= 1500)     % check if the amplitude over 1500
                a = 1;                            % estimate the garbage as plastic
                break;
            end            
        end

[Walter Roberson]

When the arduino sends the character '0', sound recording is turned on for 2 seconds. The result is written to a file and then read back from the file (a waste, might have well just used what was in memory.) After that an fft analysis is done. See the first example in the documentation of fft()