I am building a momentum indicator. would like to add more!

[KYLEM0990]

i am building a momentum indicator. it is simple
close - close(from any number of bars ago) = momentum line.
i would like to be able to selct the number of bars on a scanner for any time frame.
also i would like to have a vertical line drawn on the chart when it crosses above and below zero line with different colors for each here is what i have so far i am getting stuck on the vertical bar part.
any input on what i am missing on the how to write this would be appreciated i amy trying to learn more about the syntax

##LOL TIK TOK



declare lower;
def zeroline = 0;

def vm = close from 10bars ago;
def x = close - vm;

plot myline = x;
plot data = zeroline;

 

[Joshua]

Declare Lower;
Input Length = 10;
Plot MyLine = Close - Close[length];
Plot ZeroLine = 0;
Def cUp = MyLine crosses above 0;
Def cDn = MyLine crosses below 0;
AddVerticalLine(cUp, "A B O V E", Color.Green);
AddVerticalLine(cDn, "B E L O W", Color.Red);

Declare Upper;
Input Length = 10;
Def MyLine = Close - Close[length];
Def ZeroLine = 0;
Def cUp = MyLine crosses above 0;
Def cDn = MyLine crosses below 0;
AddVerticalLine(cUp, "A B O V E", Color.Green);
AddVerticalLine(cDn, "B E L O W", Color.Red);