sine wave with noise

Hi all

I have sine signal with noise where the number of points of noise per oscillation should be the same say five points per oscillation) , I want to change each time the number of oscillation :2,3,4….15

At each number of oscillation I shall extract the amplitude as a function of frequency < unfortunately for few oscillation FFT wouldn't work there are too few points in the signal

So how can I do that ?

See my attach code

num=50;
Fs=1000;   %sampling frequency 
Ts=1/Fs;   %sampling period or time
dt=0:Ts:1-Ts;  %signal duration
f=100;
num_points_osc=Fs/f; % number of points per oscillation
y1=sin(2*pi*f*dt);
y2=randn(1,num);
y=y1(num)+y2;
nfft=length(y);%length of time domain signal 
nfft2=2^nextpow2(nfft);%length of signal in power 2 - since it's more effecient for  fft in matlab  
ff=fft(y,nfft2);
fff=ff(1:nfft2/2);
fff=fff/max(fff);
xfft=Fs*(0:nfft2/2-1)/nfft2;
absfff=abs(fff);
figure
subplot(2,1,1);
plot(dt(1:num),y2,'.g','markersize',15);
hold on 
plot(dt(1:num),y1(1:num));
xlabel('Time [s]');
ylabel('Amplitude [v]')
title('Time Domain signal ');
subplot(2,1,2)
plot(xfft,absfff,'.-r','markersize',12);
xlabel('Frequency [Hz]');
ylabel('Normailzed Amplitude')
title('Frequency Signal Domain')