creating continues ZOH plot from samples using sinc

Hello, i have an array of dots called y_in created by the code bellow.

How using sinc function we create a continues signal of level lines(like stares) between the dots in y_in?

Thanks.

x=0.0001:0.0001:1; %10KHz ADC sampling

fb=1e3; %1Khz frequency

f_noise=4e3; %1Khz frequency

yb=sin(2*pi*fb*x); %1Khz frequency sine input signal

yf_noise=sin(2*pi*4*fb*x); %4Khz frequency sine input noise

y_in=yb+yf_noise;%total signal