Week 3 — procedures & parameters

Quiz 2 scope: Weeks 1–8 per IITM May 2026 foundation courses. Source baseline: IITM BS admissions important-dates calendar · May 2026 cycle. Times on assessments are operational conventions — verify hall ticket.

Week map

Classify → Represent → Execute → Trap-check

• Recognize: Ask: Difference between parameter and argument?
• Procedure: - Parameters
• Variations / traps: Watch for: Parameter name same as global without noticing shadowing.

Formula chain (compressed)

procedure call → parameters → local vs global → side effects.

1. Procedure — def name(params): body — reusable block
2. Call — name(args) — jump to body, return
3. Parameter — formal ↔ actual binding — per-call values
4. Return — output value to caller — expression result
5. Side effect — mutates external state — trace globals carefully

Deep study

Computational Thinking · Week 3 — Procedures and parameters

Week map

Procedure notation

• Procedure / function → named block with parameters → procedure Add(a, b).
• Parameter → placeholder in definition → a, b inside body.
• Argument → actual value at call → Add(3, 5) passes 3 and 5.
• Return → value replaces call expression → x ← Add(2, 4) → x = 6.
• Side effect → changes external state or prints → return may be absent.

text
procedure Square(n):
    return n * n

x ← 3
y ← Square(x) + 1

Return vs print (side effect)

OR selection

text
procedure Eligible(grade, score):
    if grade == "A" or score > 90:
        return True
    else:
        return False

Pattern families

Easy — Trace one call

• Substitute arguments into parameters.
• Single return to assignment.
• Parameter shadows outer name — inner definition wins inside body.

Medium — Return vs side effect

• Procedure prints but caller assigns from missing return → None-like bug.
• Mutating input list as side effect — caller’s list changes.
• Two calls in one expression: Add(1,2) + Add(3,4).

Hard — OR procedure design

• Truth table from word problem → procedure returning category.
• Nested call: Double(Square(3)).
• Parameter count mismatch at call — error or wrong binding.

Worked mini-examples

text
procedure Max2(a, b):
    if a >= b:
        return a
    else:
        return b

m ← Max2(7, 5)   # m = 7

text
procedure Weekend(day):
    if day == "Sat" or day == "Sun":
        return True
    return False

Weekend("Sat") → True
Weekend("Mon") → False

text
procedure Show(n):
    Print(n)
    # no return

x ← Show(4)   # displays 4; x not useful for math

text
procedure Inc(n):
    return n + 1

Inc(Inc(5)) → Inc(6) → 7

Traps

• Ignoring return value when assignment expected.
• Parameter name equals global variable — trace inside procedure carefully.
• Side effect mutating caller’s list without expecting it.
• OR when problem requires all conditions (AND).
• Wrong argument order if parameters positional.

Diagnostic (try yourself)

1. Trace:

text
procedure Times3(k):
    return k * 3

a ← 2
b ← Times3(a) + Times3(1)

1. Write OR condition in one line: flag True when code == 404 or code == 500.
2. Procedure prints n*n but does not return. Caller runs y ← Square(5) then z ← y + 1. What can go wrong?
3. procedure Pick(a, b): if a > 10 or b > 10: return a + b else: return 0. Evaluate Pick(3, 12) and Pick(8, 2).
4. Difference between parameter and argument in one sentence each.

ChatGPT prep archive

• Chatty reference archive

Archived import for extra depth — complements the notes above, not official IITM material.

Core concepts

• Procedure: named reusable block; parameters receive inputs per call.
• Return value replaces call expression; side effect changes external state (print, mutate list).
• OR selection: pass if any condition true—different from AND filter.
• Call stack: caller waits; callee runs; returns to caller line.

Notation & vocabulary

Pattern families

Easy — Trace a call

Medium — Return vs print

Hard — OR gate procedure

Drill these on the pattern atlas — filter to week 3.

Traps

• Parameter name same as global without noticing shadowing.
• Ignoring return value when assignment expected.
• Side effect mutating input list unexpectedly.
• OR when problem requires all conditions (AND).

Retrieval prompts

1. Difference between parameter and argument?
2. Return vs side effect example?
3. When is OR the right composite predicate?

Practice loop

1. Read Deep study (if present) or core concepts once.
2. Recite the formula chain without looking.
3. Open one easy pattern on the interactive atlas for week 3.
4. Attempt without solutions; mark studied after an honest try.
5. Say one trap aloud before closing the tab.

Related

• Full weeks 1–8 prep guide
• Pattern atlas note
• Formula chain desk