why I get error when Start my code with %?

%% Section 1

%

ka=0.8;

Am=1;

fm=2;

t=0:0.001:1;

mt=Am*sin(2*pi*fm*t);

Ac=2;

fc=50;

ct=Ac*cos(2*pi*fc*t);

St=(1+ka.*mt).*ct;

subplot (3, 1, 1)

Answer 1

[John D'Errico]

%% Section 1
% 
ka=0.8;
Am=1; 
fm=2;
t=0:0.001:1;
mt=Am*sin(2*pi*fm*t);
Ac=2;
fc=50;
ct=Ac*cos(2*pi*fc*t);
St=(1+ka.*mt).*ct;
subplot (3, 1, 1)

As you can see, there is no error. You have not plotted anything yet.

If you got an error, then show what you got, and say why you are confused about what you see.