List traversal, counts and totals

A supplied list contains -2, 0 and 3. The condition is x ≥ 3. Which of those entries passes?

Use the signed value and include equality with 3

An entry's position is not its value

A list stores entries in a stated order. Equal values may occupy different positions

In this pseudocode, positions start at 1 and L[2] means the value at the second position. Other programming languages may use a different indexing convention

The supplied list is [3, -2, 3, 3, 0, 9]. Its second position contains -2, not the number 2

Reading a position does not move, remove or change the entry

Read a negative entry without changing its sign

A list stores entries in order, including repeated values. In this pseudocode, positions start at 1 and ← means assignment

What is \(L[2]\)?

Count positions from 1. Position 2 contains -2

Locate the fourth entry

A repeated value still has its own position

FOR EACH visits entries, not distinct values

FOR EACH x IN L means that x takes each entry's value in the list's order, one visit per position

Repeated values get separate visits. A negative value or zero is still visited, even if it fails the condition inside the loop

In these examples the list stays unchanged. The variable total records a running result

Set total to its initial value before the loop. For each visit, test the current x and apply the stated update only when the condition is true

When that condition is false, total stays unchanged and the next entry is still visited. Output total after all visits

Add one for each passing entry

A list stores entries in order, including repeated values. In this pseudocode, positions start at 1 and ← means assignment

1. total ← 0
2. FOR EACH x IN L: if x ≥ 3, set total ← total + 1
3. OUTPUT total

What is the final output?

The passing entries, in order, are [3, 3, 3, 9]. The value 3 occurs 3 times and each occurrence is visited

There are 4 passing entries

Count every qualifying occurrence

The full supplied list is [3, -2, 3, 3, 0, 9]. Choose how many leading entries to process, from zero to all six. The condition stays x ≥ 3 and total starts at 0. Count uses +1; Sum uses +x. Predict each running result before changing the controls

With four leading entries selected, why does Count output 3 while Sum outputs 9?

The update determines what total means

total ← total + 1 counts one passing entry, regardless of that entry's value

total ← total + x adds the passing entry's value. A passing 9 contributes nine to this sum but only one to a count

Using the same list and condition does not make the two outputs equal

Keep a separate row for every visit when checking a trace, including rows where total does not change

Add the qualifying values rather than their positions

A list stores entries in order, including repeated values. In this pseudocode, positions start at 1 and ← means assignment

1. total ← 0
2. FOR EACH x IN L: if x ≥ 3, set total ← total + x
3. OUTPUT total

What is the final output?

The passing entries, in order, are [3, 3, 3, 9]. The value 3 occurs 3 times and each occurrence is visited

Retain repeated contributions in a sum

Process [3, -2, 3, 3, 0, 9] completely with total initially 0 and condition x ≥ 3. Algorithm A adds 1 when an entry passes. Algorithm B adds x when it passes. Which pair of final outputs is correct?

The passing entries are 3, 3, 3 and 9

No entries means no visits

An empty list has no entries. A FOR EACH loop over it executes its body zero times

The value set before the loop is therefore retained unless a separate later instruction changes it

The prefix explorer demonstrates this with total initially 0. Other supplied algorithms may state a different initial value, so read the actual givens

A separate algorithm sets total ← 7, runs FOR EACH x IN an empty list with the update total ← total + x, then outputs total. There are no other assignments. What is output?

No entry is available to trigger the loop body

A loop should total all qualifying entries, starting from zero. Where should total ← 0 occur so earlier contributions are retained?

Later visits must build on the total from earlier visits

Check a shorter supplied list without dropping repeats

Record each visit in a trace table

Teacher-reviewed written trace, not automatically assessed here

Use list [-4, 0, 2, 2, 7], condition x ≥ 2 and total initially 0

Make one row per position with columns for x, the condition result, total before the update and total after the update

Complete the table once with the count update +1 and once with the sum update +x. Explain why repeated 2 entries appear in separate rows

Add an empty-input trace and explain which initial value survives. Keep tracing a supplied algorithm separate from independently writing and testing a program

Preserve positions, visits and the meaning of the update

Read a position using the declared indexing convention, without replacing its value by its position number

Visit every listed occurrence, including repeats and entries that fail the condition

Add 1 to count entries or add x to sum their values

Initialise before the loop, retain earlier contributions and output after the required visits