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01. Concatenation

Key Vocabulary (LO AAP-2.D)

Term	Definition (write it)
String
Character
Concatenation
Substring
Position (index)

Concatenation Joins Strings End-to-End

• If you concatenate "code" and "NOW" with nothing between them, the result is .
• To make joined strings read as separate words, you must .
• "AP" + "CSP" and "CSP" + "AP" give different results because concatenation .

The Space Only Appears If You Add It

first + last runs the names together; first + " " + last inserts the space you supplied.

AP Pseudocode (what the exam tests)

first ← "Ada"
last ← "Lovelace"
DISPLAY(first + last)
DISPLAY(first + " " + last)

Python (the runnable version)

first = "Ada"
last = "Lovelace"
print(first + last)
print(first + " " + last)

Output

AdaLovelace   Ada Lovelace

Run and edit this yourself in the coding exercises for this topic.

Evaluate Each Concatenation

Give the exact string each expression produces. Watch for spaces that are — and are not — supplied.

Complete the empty cells.

Expression	Result	Why
"cat" + "dog"		joined end-to-end; no space is added for you
"cat" + " " + "dog"		the middle " " supplies the only space
"AP" + "CSP"	APCSP	left piece first, then the right piece
"CSP" + "AP"	CSPAP	swapping the operands swaps the halves
"7" + "3"		these are text characters, so they join — they are NOT added to make 10

02. Substrings

A Substring Is Part of an Existing String

• A substring is best described as .
• Taking a substring leaves the original string .
• On the exam the 3rd character is position 3, but in Python that same character is at .

Take a Piece, Leave the Original

The exam describes a substring in words (there is no SUBSTRING procedure on the reference sheet); Python takes the piece with a slice, counting from 0.

AP Pseudocode (what the exam tests)

word ← "computer"
part ← first 4 characters of word
DISPLAY(part)
DISPLAY(word)

Python (the runnable version)

word = "computer"
part = word[0:4]
print(part)
print(word)

Output

comp   computer

Run and edit this yourself in the coding exercises for this topic.

Read the Substring by Position

Using exam positions (counting from 1), give the substring each description names. The last column shows the matching Python index.

Complete the empty cells.

Word	Take...	Substring	Python index note
rainbow	the first 3 characters		positions 1–3 = indexes 0–2
rainbow	the 4th character		position 4 = index 3
rainbow	the last 3 characters	bow	positions 5–7 = indexes 4–6
science	the 3rd character		position 3 = index 2

Common AP Traps

Three ways Topic 3.4 loses points on the exam — one minute now, real points in May.

Concatenation adds no spaces — in your own words:

Order matters, and the originals survive — in your own words:

Position base: exam counts from 1, code from 0 — in your own words:

Strings, in One Slide

• String concatenation joins two or more strings end-to-end to make one new string, and it adds no spaces of its own.
• Concatenation preserves operand order and leaves the original strings unchanged — "AP" + "CSP" ≠ "CSP" + "AP".
• A substring is part of an existing string — one or more of its characters — and taking it does not change the source.
• Character positions differ by base: the exam reference sheet counts from 1, while Python and JavaScript count from 0.