Faulty Algorithm?

Computer Science Level 2

Alex wants to create an algorithm to calculate the sum of the first 100 positive integers.

He tells the algorithm to
1. Create the variable sum with an initial value of 0.
2. Start with the value of $i = 1$
3. Add $i$ to the sum
4. Add 1 to $i$
5. Continue doing so till $i = 100$

Does this algorithm work?

No, it should sum till

i = 101

. No, it should sum till

i = 99

. No, it should add 2 to

i

. Yes it works perfectly.

1 solution

Brock Brown
Jun 19, 2015

Alex's algorithm will only sum the first $99$ positive integers. The part where $i$ is added to sum is located before the part where $1$ is added to $i$ , so the loop ends before it gets a chance to add $100$ to sum .

And of course, here is some Python:

Python 3.4:

# Alex's algorithm
sum = 0
i = 1
while i != 100:
    sum += i
    i += 1
print("i =", i)

Faulty Algorithm?

1 solution

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