# Sum of N numbers using a while loop in Python Last updated: Jul 4, 2022 Photo from Unsplash

## Sum of N numbers using a while loop in Python#

To get the sum of N numbers using a while loop:

1. Iterate for as long as the number is greater than `0`.
2. On each iteration, decrement the number by `1`.
3. On each iteration, increment the total by the number.
main.py
```Copied!```sum_of_numbers = 0

num = 5

while num > 0:
# 👇️ reassign sum to sum + num
sum_of_numbers += num

# 👇️ reassign num to num - 1
num -= 1

print(sum_of_numbers)  # 👉️ 15  (5 + 4 + 3 + 2 + 1)

print(num)  # 👉️ 0
``````

The `while` loop in the example iterates for as long as the `num` variable stores a value greater than `0`.

On each iteration, we use the `+=` operator to reassign the `sum_of_numbers` variable to its current value plus `num`.

To move towards the base case, we also use the `-=` operator to reassign the `num` variable to its value minus `1`.

The following 2 lines of code achieve the same result:

• `sum_of_numbers += num`
• `sum_of_numbers = sum_of_numbers + num`

Similarly, the `-=` operator is also a shorthand:

• `num -= 1`
• `num = num - 1`
Make sure to specify a base case that has to be met to exit the `while` loop, otherwise you might end up with an infinite loop.

A commonly used alternative is to use a `while True` loop with a `break` statement.

main.py
```Copied!```sum_of_numbers = 0

num = 5

while True:
# 👇️ reassign sum to sum + num
sum_of_numbers += num

# 👇️ reassign num to num - 1
num -= 1

# 👇️ if num is equal to or less than `0`, break out of loop
if num <= 0:
break

print(sum_of_numbers)  # 👉️ 15  (5 + 4 + 3 + 2 + 1)

print(num)  # 👉️ 0
``````

The `while True` loop iterates until it is interrupted by a `break` statement.

The loop is quite similar to the previous example, however we manually check if the `num` variable stores a value of less than or equal to `0` on each iteration.

Which approach you pick is a matter of personal preference. I'd go with using the `while` loop from the first example as I find it more intuitive and easier to read.

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