Plotting loops, but only empty plot

I'm trying to plot the information from my loops, but all I am getting is an empty plot. My code is as follows:

x1 = 1;
   while  x1<19;
    y1(x1)=x1^3-(5*x1)^2+2^x1-10000*x1;
    x1=x1+1;
   end

for x2=1:20
  y2(x2)=20000*log(x2)-3*x2;
  x2=x2+1;
end

%Create the plot
figure
   plot(x1,y1,'b-',x2,y2,'k-')

Answer 1

[Star Strider]

Add ‘x’ as an index to create your ‘x1’ vector, and specify x2 as a vector outside the loop:

x = 1;
   while  x<19;
    x1(x) = x;
    y1(x)=x1(x)^3-(5*x1(x))^2+2^x1(x)-10000*x1(x);
    x=x+1;
   end

for x2=1:20
  y2(x2)=20000*log(x2)-3*x2;
end
x2=1:20;

%Create the plot
figure
   plot(x1,y1,'b-',x2,y2,'k-')