CODEWITHSUNDEEP
rwhile-loop
user3922546
user3922546

Reputation: 187

simple while loop in r going into infinite loop

I'm trying to write a R program to calculate the sum of a geometric series without using the standard formula as shown below:

h <- function(x,n){
    sum.value <- 1
          i <- 1
       while ( i <= n){
          sum.value = sum.value + x^i
      }
return(sum.value)
}

When I run this code, it goes into an infinite loop. I didn't have trouble when running it using a for loop. Its really strange that the same doesn't work with a while loop as is said that a while loop is more fundamental that a for loop. Have I missed something? Thanks.

Upvotes: 1

Views: 5477

Answers (2)

asdfasdf
asdfasdf

Reputation: 100

A for loop in R increments automatically. A while loop does not. You need to add an increment to i inside your while loop if you want it to work.

Upvotes: 1

Roland
Roland

Reputation: 132576

You forgot to increase i. Also I don't understand why sum.value starts with 1.

h <- function(x,n){
  sum.value <- 0
  i <- 1
  while ( i <= n){
    sum.value = sum.value + x^i
    i <- i+1
  }
  return(sum.value)
}

h(3,5)
#[1] 363

Of course, it would be much more efficient and simpler to use vectorization:

sum(3^(1:5))
#[1] 363

Upvotes: 3

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