Digital Signal Processing, DSP

Who can help me ? I have a task.

1. Make a sinusoid. User gives amplitude and frequency (input command). 2. Sampling - two periods (Shannon-Kotelnikov theorem) 3. Quantization with 3-bit converter 4. 8 the least significant bit's - change to HEX and DEC

I tried all last week and nothing. This is all what I did:

clear all
close all

a = input(Amplitude: ');
f = input('Frequency: ');

fp = 100*f; 
N = 2*100; 

T1 = N/fp;
t1 = (0:N-1)/fp;
s1 = a*sin(2*pi*f*t1);

fp = 2*f  

s2 = s1(1:N/fp:end);
t2 = (0:length(s2)-1)/fp;

plot(t1,s1)
hold
stem(t2,s2,'rx')
hold
xlabel('Time [s]')
ylabel('Amplitude')