# R Program to Find the Sum of Natural Numbers

In this example, you’ll learn to find the sum of natural numbers entered by the user. The example uses a while loop to calculate the sum.

To understand this example, you should have the knowledge of following R programming topics:

## Example 1: Find sum of natural numbers without formula

``````# take input from the user
num = as.integer(readline(prompt = "Enter a number: "))
if(num < 0) {
print("Enter a positive number")
} else {
sum = 0
# use while loop to iterate until zero
while(num > 0) {
sum = sum + num
num = num - 1
}
print(paste("The sum is", sum))
}
``````

Output

```Enter a number: 10
[1] "The sum is 55"
```

Here, we ask the user for a number and display the sum of natural numbers upto that number.

We use `while` loop to iterate until the number becomes zero. On each iteration, we add the number num to sum, which gives the total sum in the end.

We could have solved the above problem without using any loops using a formula.

From mathematics, we know that sum of natural numbers is given by

`n*(n+1)/2`

For example, if n = 10, the sum would be (10*11)/2 = 55.

## Example 2: Find sum of natural numbers using a formula

``````# take input from the user
num = as.integer(readline(prompt = "Enter a number: "))
if(num < 0) {
print("Enter a positive number")
} else {
sum = (num * (num + 1)) / 2;
print(paste("The sum is", sum))
}
``````

Output

```Enter a number: 10
[1] "The sum is 55"
```