Root Mean Square
Example of loop usage: calculation of Root Mean Square (en.wikipedia.org/wiki/Root_mean_square).
//@version=2
study("Root Mean Square", shorttitle="RMS")
// https://en.wikipedia.org/wiki/Root_mean_square
src = input(close)
sum = 0
len = input(10)
for i = 0 to len
sum := sum + src[i]*src[i]
res = sqrt(sum/len)
plot(res)