Sum of n numbers in Python using while loop

In this post, you will learn how to find the sum of n natural numbers using a while loop in Python programming language. The while loop in Python is used to iterate over a block of code as long as the truth expression (condition) is true.

In the given example, we have used the if..else statement in combination with a while loop to calculate the sum of n numbers. First, we have taken a number input from the user and stored it in a variable num. Initially, the sum is initialized to 0. The while loop is then used to iterate until the num equals zero. In every iteration of the loop, we have added the num to the sum, and the value of the num is decreased by 1.

# Sum of natural numbers up to num

num = int(input("Enter a number: ")) 

if num < 0:
   print("Please enter a positive number")
else:
   sum = 0
   
   # use while loop to iterate until zero
   while(num > 0):
       sum += num
       num -= 1
   print("The result is", sum)

Enter a number: 15
The result is 120

The above example shows the sum of the first 15 positive numbers (0-15).

Enter a number: 22
The result is 253

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