Writing own test in R (mean test) - r

Question

i need to write an own test in R with the help of the mean of a given test statistic of 2 given random variables X and Y which are unknown distributed.
I am given following code:
mean.test <- function(x, y, B=10000,
alternative=c("two.sided","less","greater"))
{
p.value <- 0
alternative <- match.arg(alternative)
s<-replicate(B, (mean(sample(c(x,y), B, replace=TRUE))-mean(sample(c(x,y), B, replace=TRUE)))) # random samples of test statistics
t <- mean(x) - mean(y) #teststatistics t
p.value <- 2 * (1- pnorm(mean(s))) #try to calculate p value
data.name <- deparse(substitute(c(x,y)))
names(t) <- "difference in means"
zero <- 0
names(zero) <- "difference in means"
return(structure(list(statistic = t, p.value = p.value,
method = "mean test", data.name = data.name,
observed = c(x,y), alternative = alternative,
null.value = zero),
class = "htest"))
}
Where t is the mean of a random set of the variables X and Y substracted from each other. I am given some solution to some function calls, but i never get them.
For example following:
set.seed(0)
mean.test(rnorm(100,50,4),rnorm(100,51,5),alternative="less")
Should output:
mean test
data: c(rnorm(100, 50, 4), rnorm(100, 51, 5))
difference in means = -2.0224, p-value = 0.0011
alternative hypothesis: true difference in means is less than 0
But it outputs:
mean test
data: c(rnorm(100, 50, 4), rnorm(100, 51, 5))
difference in means = -0.68157, p-value = 1
alternative hypothesis: true difference in means is less than 0
I am sure that i am calculating the p value in a wrong way. Also the mean values substracted from each other are wrong for this example, but right for other examples of the excercise. I am really confused as how to calculate the p value. How do i calculate it?