# 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"