Exercise 8: Running Totals from a List of Tuples — Possible Solution
====================================================================

transactions = [
    ("food", 12.50),
    ("transport", 3.20),
    ("food", 8.00),
    ("entertainment", 15.00),
    ("transport", 2.80),
]

totals = {}
index = 0

while index < len(transactions):
    category, amount = transactions[index]

    if category in totals:
        totals[category] += amount
    else:
        totals[category] = amount

    index += 1

print(totals)

Output:
{'food': 20.5, 'transport': 6.0, 'entertainment': 15.0}

WHY THIS WORKS AS AN ANSWER
------------------------------
transactions[index] retrieves one (category, amount) tuple at a time,
and category, amount = transactions[index] unpacks it into two named
variables in one line — the same unpacking technique from the tuples
lesson, just applied inside a while loop instead of a for loop.

The accumulation logic is identical to Exercise 3's counting pattern
(check whether the key exists yet, then either start it or add to it) —
the only difference is adding a variable amount instead of always
adding a fixed 1. Recognising that these are "the same pattern" is the
real skill here: a huge number of real-world aggregation problems are
just this one idea (initialise-or-accumulate keyed by some category)
applied to whatever data you're actually working with.