You haven't used the right syntax for your for loop and if statement.  After the for loop you need an open curly bracket instead of a semicolon and then some more code inside that will be repeated (for single lines you can get away without the brackets but it's better if you learn the full syntax to start with).  Your if statement has a similar problem.  Have a look at the tutorial pages on iteration and conditionals for examples of how the code should look and post back if you get stuck.

Compare the code below to lines 13 and onwards in your code  After the for loop there are additional commands inside the curly braces that are looped, in your code there's just a semicolon which is the equivalent of saying "while barx is less than or equal to bary don't do anything."  Your if statement has the same problem - after the conditional statement there are no commands.

1.   for (int x =barX; barX<=barY;barX ++) {
2.     if (random (0, 2)>=1) {
3.       line(barX, barY, barX, lineY);
4.     }
5.   }

Yes, looking at it there's still quite a lot wrong with what you've written.  This is the for loop you have:

1. for (int x =barX; barX<=barY;barX ++)

What that's saying is create a variable called x and set it equal to barX; loop over the following code until barX is equal to barY and each loop increment barX.  There are a couple of issues with that.  Why are you creating a variable called x that you never use again?  What's going to happen when you loop while barX is less than or equal to barY?  You've got a variable called barWid but you're not taking it into account anywhere.

This works:

1. void drawBarCode(int barX, int barY, int barWid, int barHei) { 
2.   rect(barX, barY, barWid, barHei);
3.   int lineY = barY+barHei;
4.   for (int x = barX; x <= barX + barWid; x++) {
5.     if (random(0, 2) >= 1) {
6.       line(x, barY, x, lineY);
7.     }
8.   }
9. }