Add up the numbers 1 to 100 in Python.

The program

Press Run to see what it prints. Change anything you like, then run it again.

total = 0
for n in range(1, 101):
    total = total + n
print("The sum is", total)
print("Check with the formula:", 100 * 101 // 2)
print("Using sum():", sum(range(1, 101)))

The sum is 5050
Check with the formula: 5050
Using sum(): 5050

How it works

1. total starts at 0 and grows each time round the loop. This pattern is called an accumulator.
2. The story goes that the mathematician Gauss, as a schoolboy, found this sum quickly by pairing 1 with 100, 2 with 99 and so on: 50 pairs of 101, which is 5,050.
3. sum() adds up a list or range for you. // is division that gives a whole number.

Try this

• Add up only the even numbers.
• Add up the squares: 1, 4, 9, ... up to 100.
• Find the formula for the sum from 1 to any n.

Stuck on an error? Read how to debug Python.