Practice Variable in CS Thinking

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

A named container in a program that stores a value, which can be read, updated, or replaced. Variables have a name (identifier), a value (the data stored), and in many languages a type (what kind of data it holds).

A labeled box you can put things in, take things out, or change what's inside.

Showing a random 20 of 50 problems.

Example 1

easy

Which is a clearer variable name for a person's age: 'x' or 'age'?

Example 2

easy

Using a variable before assigning it any value typically causes what kind of error?

Example 3

easy

A variable's ____ tells the program what kind of data it holds (e.g., int, string).

Example 4

easy

Trace:

s =

'cat';

s = s + 's'

. Final

s

Example 5

medium

Trace:

x = 1

;

y = x

;

x = x + y

;

y = x + y

. Final

x, y

Example 6

medium

Trace swap without a temp using arithmetic:

a=7

;

b=3

;

a=a+b

;

b=a-b

;

a=a-b

. Final

a, b

Example 7

easy

Trace:

a = 10

;

a = a - 3

. Final

a

Example 8

medium

Trace:

a, b = 3, 5

;

a, b = b, a

. Final

a, b

Example 9

easy

In 'total = price', which side receives the value: total or price?

Example 10

hard

In a scope-aware language,

x = 1

is defined globally and a function sets

x = 2

locally. After the function returns, what is the global

x

Example 11

challenge

Trace:

x=2

; for

i

in range(3):

x = x * x

. Final

x

(range(3) is 3 passes)?

Example 12

easy

Which variable name is clearer for a student's grade: 'g' or 'grade'?

Example 13

challenge

Trace:

a=1

;

b=2

;

c=3

;

a=b

;

b=c

;

c=a

. Final

a,b,c

Example 14

medium

Trace:

a = 5

;

b = a + 1

;

a = b + 1

;

b = a + 1

. Final

a, b

Example 15

easy

What is the output? SET score = 0. SET score = score + 10. SET score = score + 5. OUTPUT score.

Example 16

easy

Trace:

x = 3

;

y = x

;

x = 99

. Final

y

Example 17

medium

Trace:

x = 3

;

y = x * 2

;

x = 10

;

z = x + y

. Final

z

Example 18

medium

Trace:

a=2

;

b=3

;

a=b

;

b=a

. Final

a

and

b

— does this swap them?

Example 19

easy

What is wrong with:

\text{print}(x)

;

x = 5

Example 20

medium

Trace:

count=0

; for

v

[1,2,3,4,5]

: if

v\%2==1

count = count + 1

. Final

count

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