Runif Help: same variable, 3 different parameters

So I am working on an economic model and I need to change the parameters of
the runif statement as time goes on.

Ex.

X<-runif(1:50,0,5)
X<-runif(51:100,100,150)
X<-runif(100:T, 1,2)

Not sure how to go about entering this in to R properly.

It's not clear what you are trying to do.  The first argument to runif 
only selects the sample size.  In your first two cases, you'll get 
samples of size 50; in the last one, you'll get a sample size depending 
on T in a nonlinear way.

Duncan Murdoch