Parameters Examples in CS Thinking
Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Parameters.
This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in CS Thinking.
Concept Recap
Named values declared in a function definition that act as placeholders for the actual data (arguments) passed in when the function is called. Parameters allow the same function to operate on different data each time it is invoked.
The blanks you fill in when using a function. Like a form with fields.
Read the full concept explanation →How to Use These Examples
- Read the first worked example with the solution open so the structure is clear.
- Try the practice problems before revealing each solution.
- Use the related concepts and background knowledge badges if you feel stuck.
What to Focus On
Core idea: Parameters make functions flexible—same code, different data.
Common stuck point: Parameter (in definition) vs. argument (in call)—often used interchangeably.
Sense of Study hint: When defining parameters, give each one a clear name that describes what data it expects. When calling the function, make sure you pass arguments in the correct order and of the correct type. If a function has many parameters, consider grouping related ones into an object.
Worked Examples
Example 1
easyWhat is the output of the following? FUNCTION greet(name): OUTPUT 'Hello, ' + name. greet('Alice'). greet('Bob').
Answer
Hello, Alice then Hello, Bob.
First step
1
Step 1: When greet('Alice') is called, the parameter name takes the value 'Alice'.
Full solution
- 2 Step 2: The function outputs 'Hello, ' + 'Alice' = 'Hello, Alice'.
- 3 Step 3: When greet('Bob') is called, name = 'Bob', so it outputs 'Hello, Bob'. Parameters allow the same function to work with different inputs.
Parameters are variables listed in a function definition that receive values (arguments) when the function is called. They make functions reusable with different data.
Example 2
mediumFUNCTION calculateArea(length, width): RETURN length * width. What is calculateArea(5, 3)? What happens if you call calculateArea(5) with only one argument?
Example 3
easyPattern: same function, different arguments. `def square(n): return n*n`. Trace `square(3)`, `square(7)`, `square(10)`.
Example 4
mediumTrace: `def push(items, x): items.append(x); return items`. After `lst=[1,2]; push(lst, 9)`, what is `lst`?
Example 5
mediumSame code, different data. `def total(prices, tax): return sum(prices) * (1 + tax)`. Compute `total([10, 20, 30], 0.1)`.
Example 6
hardTrace: `def f(n, acc=0): if n == 0: return acc; return f(n-1, acc+n)`. What is `f(4)`?
Example 7
challengeDesign a function `clamp(value, lo=0, hi=100)` that returns value bounded between lo and hi. Trace `clamp(150)` and `clamp(-3, lo=-10, hi=10)`.
Practice Problems
Try these problems on your own first, then open the solution to compare your method.
Example 1
mediumWrite a function called power(base, exponent) that returns base raised to the exponent using a loop. Trace power(2, 4).
Example 2
hardExplain the difference between passing by value and passing by reference. If FUNCTION double(x): x = x * 2 is called with SET a = 5. double(a), what is the value of a after the call in each case?
Example 3
easyIn `def f(name): print(name)`, what is `name`?
Example 4
easy`def f(a, b): return a - b`. What is `f(10, 3)`?
Example 5
easy`def f(a, b): return a - b`. What is `f(3, 10)`?
Example 6
easyHow many parameters does `def f(x, y, z): return 0` have?
Example 7
easy`def f(a, b=5): return a + b`. What is `f(2)`?
Example 8
easyWhat is the difference between a parameter and an argument in `f(x)` called as `f(7)`?
Example 9
easy`def f(a, b, c): return a`. What does `f(1, 2, 3)` return?
Example 10
easyCalling `def f(a, b): return a+b` as `f(5)` causes what?
Example 11
medium`def f(a, b, c): return a + 2*b + 3*c`. What is `f(1, 2, 3)`?
Example 12
mediumUsing keyword arguments, `def f(a, b): return a - b` called as `f(b=2, a=10)` returns what?
Example 13
medium`def f(*nums): return sum(nums)`. What is `f(1, 2, 3, 4)`?
Example 14
medium`def scale(x, factor=2): return x*factor`. Calls: `scale(5)`, `scale(5, 3)`. What are the two results?
Example 15
mediumWhy does passing `f(2, 3)` to `def f(width, height): return width*height` work, but the variable names at the call site don't matter?
Example 16
medium`def f(a, b): a = a + 1; return a + b`. After `x = 5; f(x, 1)`, what is `x`?
Example 17
medium`def f(a, b, c=0): return a+b+c`. Which call is INVALID: `f(1,2)`, `f(1,2,3)`, `f(1)`?
Example 18
challenge`def swap(a, b): a, b = b, a` is called as `swap(x, y)` with `x=1, y=2`. After the call, what are `x` and `y`?
Example 19
challenge`def f(items=[]): items.append(1); return len(items)`. What does the THIRD call `f()` return?
Example 20
challengeA function takes 4 parameters: `(host, port, user, password)`. Why is calling it with keyword arguments safer than positional?
Example 21
medium`def f(a, b, c): return c`. Called as `f(1, 2, 3)`, what is returned?
Example 22
medium`def f(a, b): return a * 10 + b`. What is `f(3, 7)`?
Example 23
easy`def add(x, y): return x + y`. What is `add(4, 6)`?
Example 24
easyHow many parameters does `def area(base, height): return 0.5*base*height` have?
Example 25
easy`def greet(name): return 'Hi ' + name`. What does `greet('Sam')` return?
Example 26
easy`def first(a, b, c): return a`. What does `first(7, 8, 9)` return?
Example 27
medium`def f(a, b, c=10): return a + b + c`. What is `f(1, 2)`?
Example 28
medium`def f(a, b, c=10): return a + b + c`. What is `f(1, 2, 5)`?
Example 29
medium`def div(a, b): return a // b`. What is `div(20, 6)`?
Example 30
medium`def f(a, b): return a - b`. What does the keyword call `f(b=10, a=3)` return?
Example 31
medium`def f(a, b): a = a + 100; return a + b`. After `x=5; result = f(x, 1)`, what are `x` and `result`?
Example 32
medium`def f(*args): return len(args)`. What does `f(10, 20, 30, 40)` return?
Example 33
medium`def speed(distance, time): return distance / time`. A function is meant to compute speed but is called as `speed(2, 60)` when the values are 60 km and 2 hours. What is the bug?
Example 34
medium`def f(a, b, c): return (a + b) * c`. What is `f(2, 3, 4)`?
Example 35
medium`def f(name, age=12, grade='A'): return f"{name}-{age}-{grade}"`. What does `f('Lee', grade='B')` return?
Example 36
hard`def f(x, lst): lst.append(x); x = x + 1; return x`. After `a = 5; b = []; r = f(a, b)`, what are `a`, `b`, `r`?
Example 37
hard`def add_item(item, bag=[]): bag.append(item); return bag`. What do the FIRST two calls `add_item(1)` then `add_item(2)` return?
Example 38
hardA function `connect(host, port, user, password)` is called as `connect('db', 'admin', 5432, 'pw')`. Why is this dangerous, and what is the safer call?
Example 39
hard`def f(a, b, *rest): return a + b + sum(rest)`. What is `f(1, 2, 3, 4, 5)`?
Example 40
challenge`def f(x, y=x+1): return y`. Why does this definition raise an error at definition time?
Related Concepts
Background Knowledge
These ideas may be useful before you work through the harder examples.
function