Looping over an array

Loop over an array with for and compute a sum.

Searching in an array

To find a specific element in an array, use linear search: check each element in order. The worst case is O(n).

If the element is found, its index is returned; if not, -1 is returned. This does not require the array to be sorted.

To update an element, write arr[i] = new_value. This takes O(1) time because access is by index directly.

Updating does not change the array's size in memory; it only changes the value of one element.

Write sum_all(arr). Sum elements with for and return. Print 12 with print(sum_all([2, 4, 6])).

Show example solution

def sum_all(arr):
    # Compute sum
    total = 0
    for x in arr:
        total = total + x
    return total
print(sum_all([2, 4, 6]))

Update

Update the second element: arr[1] = ____

Show answer

Update the second element: arr[1] = 42