Reading Pseudocode

What This Lesson Covers

The AP CSP exam uses its own language-agnostic pseudocode — not Python, not Java. The good news: you get the full reference sheet on the exam. You don't have to memorize syntax. You just have to read it confidently.

This lesson is a fast tour of every section of the reference sheet, with the gotchas that trip up most students.

1. The AP Reference SheetProvided on the exam

The College Board provides a Reference Sheet at the start of the exam booklet. It explains every pseudocode instruction you might see. It is not a list of code to memorize — it is your dictionary while answering questions.

The reference sheet has both a text format (what we'll use here) and a block format (drag-and-drop blocks like Scratch). Both formats show up on the exam. They mean the same thing — only the appearance differs.

Open the AP CSP Reference Sheet (PDF)

This is the exact reference sheet you'll have printed in your exam booklet. Open it in another tab and keep it handy as you work through this lesson.

2. Assignment vs. Equality

This is the #1 source of student confusion on AP CSP code questions:

Other "actions": DISPLAY and INPUT

• DISPLAY(expression) — prints the value, followed by a space.
• INPUT() — pauses and returns whatever the user types.

3. Arithmetic Operators

Standard math: +, -, *, /. Normal order of operations. Plus two special ones:

4. Comparison & Boolean Operators

Comparison (yes/no questions)

These all produce a Boolean (true or false):

Boolean combinators

5. Selection: IF and IF / ELSE

IF(condition)
{
    <block of statements>
}

Run the block only if the condition is true. Otherwise, skip it entirely.

IF(condition)
{
    <first block>
}
ELSE
{
    <second block>
}

Run the first block if the condition is true; otherwise run the second block. Exactly one of the two blocks runs.

Line 1: xCount ← 0
Line 2: yCount ← 0
Line 3: REPEAT 100 TIMES
Line 4: {
Line 5:     IF(RANDOM(1, 4) = 1)
Line 6:     {
Line 7:         xCount ← xCount + 1
Line 8:     }
Line 9:     IF(RANDOM(1, 4) > 1)
Line 10:    {
Line 11:        yCount ← yCount + 1
Line 12:    }
Line 13: }

6. Iteration: REPEAT and FOR EACH

7. Lists

So for aList ← [10, 20, 30]:

• aList[1] is 10 (first element)
• aList[2] is 20
• aList[3] is 30 (last element)
• aList[0] — error! the program terminates.

List operations

8. Procedures and RETURN

PROCEDURE procName(parameter1, parameter2, ...)
{
    <block of statements>
    RETURN(expression)
}

A procedure is a named, reusable block of code that takes inputs (called parameters) and may return a result.

Calling a procedure

• procName(arg1, arg2) — runs the procedure with those arguments.
• result ← procName(arg1, arg2) — runs it and stores the returned value in result.

Line 1: PROCEDURE isIncreasing(numberList)
Line 2: {
Line 3:     count ← 2
Line 4:     REPEAT UNTIL(count > LENGTH(numberList))
Line 5:     {
Line 6:         IF(numberList[count] < numberList[count - 1])
Line 7:         {
Line 8:             RETURN(true)
Line 9:         }
Line 10:        count ← count + 1
Line 11:    }
Line 12:    RETURN(false)
Line 13: }

9. Robot Commands

Some exam questions use a small robot in a grid. The reference sheet defines four commands:

10. How to Trace Code Like a Pro

"Trace tables" turn confusing code into a simple ledger. The trick: pick a fresh sheet of scratch paper, draw one column per variable, and write down every value as it changes.

Example trace

x ← 3
y ← 5
REPEAT 3 TIMES
{
    x ← x + y
    y ← y - 1
}
DISPLAY(x)

Misconception Lightning Round

Click True or False:

What's NOT on the AP CSP Exam

Don't spend study time on these — they're real programming concepts but they're not tested:

• Memorizing Python, Java, or JavaScript syntax Out of scope
• Object-oriented programming, classes, inheritance Out of scope
• Pointers, memory management, types beyond {number, Boolean, string, list} Out of scope
• Recursion as a tested topic (it can show up incidentally, but is not on the framework) Out of scope
• Specific sorting algorithm names (bubble sort, quicksort, etc.) Out of scope
• Big-O notation specifics — you only need "reasonable time" vs. "not reasonable time" Out of scope

Translation: The exam is testing whether you can read code, not whether you can write a specific language. Reference sheet + tracing skill = most pseudocode questions.