Why is conversion not working?

x <- data.frame(month=as.character(sample(1:12,1000,TRUE)),

# convert to integer
x$Year <- as.integer(x$year)
# now add the century
x$Year <- ifelse(x$Year < 10, x$Year+2000, x$Year+1900)


head(x)

I have a data frame, where two last columns - "month" and "year" - are
character vectors. The "year" vector is made of two numbers (i.e. "97"
for 1997, "07" for 2007, etc)
What I want to do is to create a variable "Year" that is mode numeric
and where each record is a four-figure number (1997, 2007,...)
I have about 40000 rows in the dataframe, the observations are for 10
years (so there are multiple rows for each year).
I tried the following, but the program runs and runs, and if I abort
it all the years in "Year" are 1997:

for(i in 1:dim(database)[1]){
   if(database$year[i]>90) {
          database$Year[i] <- as.numeric(database$year[i])+1900 } else {
          database$Year[i] <- as.numeric(database$year[i])+2000
   }
}

Thanks in advance for explanations.

Regards,
JM

--
Jonas Malmros
Stockholm University
Stockholm, Sweden