how to extract pitch of the audio signal?

hi. i need to extract pitch of the signal whom frequency and time i already have extracted. but when i apply pitch function of the audio processing toolbox , its not working. As it is installed but still i have to buy it or use its trial version. Is there any alternate toolbox for pitch calculation or any other way to get this toolbox. waiting for the help. code for pitch is given below:

if true
  [audioIn,fs] = audioread('hasilwav4.wav');
  [f0,idx] = pitch(audioIn,fs);
  figure
  subplot(2,1,1)
  plot(audioIn)
  ylabel('Amplitude')
  subplot(2,1,2)
  plot(idx,f0)
  ylabel('Pitch (Hz)')
  xlabel('Sample Number')
end

[KALYAN ACHARJYA]

Check here

[sidra Rafique]

this is the graph of my required sound pitch. i dont understant either its right or wrong. because its most values are zero. please help me in understanding it.

[sidra Rafique]

My code is given below for the above plot:

if true spectrum = pwelch(VE); figure plot(10*log10(spectrum)) ylabel('Pitch (Hz)') xlabel('Sample Number') end