if-else is not producing the expected output in R

I have a string:

> all_scn[1]
[1] "Cars_20160601_01.hdf5"

I want to use it to repeat some numbers based on a variable last_step:

> last_step
[1] 439

if-else statement:

> ifelse(substring(all_scn[1], 1, 1)=="C",
         rep(seq(0, last_step-1, 1), 13),
         rep(seq(0, last_step-1, 1), 12))  
[1] 0  

But you see that instead of repeating a numeric vector of 0:438, 13 times, it just produces zero. Outside ofifelse I get following:

> rep(seq(0, last_step-1, 1), 13)
   [1]   0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28
  [30]  29  30  31  32 . . .  (I truncated the output due to space limitation)

What am I doing wrong?