Variables Explore

Unit 4 - Lesson 1
Variables Explore

Computer Science Principles

Unit 4 Lesson 1 - Warm Up

Do This:
● Navigate to Lesson 1,

Levels 3-5 on Code Studio

Open Ended

These are samples of the kinds of apps you'll be able to build by the end of this unit. Write down at least two examples where the apps seems to be keeping track of a piece of information or using it to make decisions.

Warm Up

• Last unit we built apps that mostly focus on input and output

  • When button is clicked --> show picture

  • When button is clicked --> change screen

  • When button is clicked --> play a sound

• In this unit, we are going to build apps to keep track of information and use that information to make decisions and perform calculations

Warm Up

• The Pet Rock App keeps track of clicks and uses it to decide when the pet rock will "evolve"

• The Poem App keeps track of the poem as you write it

• The Thermostat App keeps track of temperature and uses it to change the color of the text

“hi”

“hi there”

“c u l8r”

Strings
Made of any characters
Inside double quotes

548

Numbers
Made of the digits 0...9
No quotes

Value

One piece of information

Goes on a sticky

“123”

Unit 4 Lesson 1 - Activity

9

22

123

​

Open Ended

Give an example of one string and one number.

2

3

Operators
Fancy name for + - * /

Expression
Combination of operators and values
Evaluates to single value

+

evaluates to

1

-

Unit 4 Lesson 1 - Activity

5

​

3

4
evaluates to
+

7

5

2
evaluates to
-

3

“for”

“ever”
evaluates to
+

“forever”

“gr”

8
evaluates to
+
“gr8”

2

“day”
evaluates to
+
“2day”

4

5

+

10

9

-

“tree”

“house”

+

“you”

“r”

+

3

“D”

+

11

2
evaluates to
*

22

10

2
evaluates to
/

5

Unit 4 Lesson 1 - Activity

9

1

"treehouse"

“your”

“3D”

​

​

Open Ended

Evaluate these expressions

3

4
evaluates to
+

7

5

2
evaluates to
-

3

“for”

“ever”
evaluates to
+

“forever”

“gr”

8
evaluates to
+
“gr8”

2

“day”
evaluates to
+
“2day”

4

5

+

10

9

-

“tree”

“house”

+

“you”

“r”

+

3

“D”

+

11

2
evaluates to
*

22

10

2
evaluates to
/

5

Unit 4 Lesson 1 - Activity

9

1

"treehouse"

“your”

“3D”

​

​

woop

2

zip

“hi”

Variables

●

Plastic baggies

●

Can hold at most one value

●

Name uses no quotes,
includes no spaces, and
must start with a letter

zip2

Unit 4 Lesson 1 - Activity

Open Ended

Give an example of a variable name

bop

zip
5

“hi”

3

bop + zip

“hi5”
evaluates to
“hi”

+

5

+ zip

Make a copy of the
value in zip. Don’t take
the sticky out of zip.

Unit 4 Lesson 1 - Activity

Open Ended

Evaluate these expressions. Make sure you pay attention to whether it evaluates to a string or a number.

3

4
evaluates to
+

7

5

2
evaluates to
-

3

“for”

“ever”
evaluates to
+

“forever”

“gr”

8
evaluates to
+
“gr8”

2

“day”
evaluates to
+
“2day”

4

5

+

10

9

-

“tree”

“house”

+

“you”

“r”

+

3

“D”

+

11

2
evaluates to
*

22

10

2
evaluates to
/

5

Unit 4 Lesson 1 - Activity

9

1

"treehouse"

“your”

“3D”

​

​

pow

var
Creates a new variable
Grab a new baggie
Writes the variable’s name on the baggie

00 var pow

Command to
create variable

Variable’s name

Line number

Unit 4 Lesson 1 - Activity

00 var pow

01 pow ← 3

02 pow ← 5

pow

pow

pow

3

5

3

Unit 4 Lesson 1 - Activity

Open Ended

Run this program. What would be stored in the pizza and tacos variables?

3

4
evaluates to
+

7

5

2
evaluates to
-

3

“for”

“ever”
evaluates to
+

“forever”

“gr”

8
evaluates to
+
“gr8”

2

“day”
evaluates to
+
“2day”

4

5

+

10

9

-

“tree”

“house”

+

“you”

“r”

+

3

“D”

+

11

2
evaluates to
*

22

10

2
evaluates to
/

5

Unit 4 Lesson 1 - Activity

9

1

"treehouse"

“your”

“3D”

​

​

00 var pow

02 pow ← 3 + 4

pow

pow

pow

3

7

3

Evaluate expression first

Unit 4 Lesson 1 - Activity

Open Ended

Run this program. What would be stored in the fly and zow variables?

3

4
evaluates to
+

7

5

2
evaluates to
-

3

“for”

“ever”
evaluates to
+

“forever”

“gr”

8
evaluates to
+
“gr8”

2

“day”
evaluates to
+
“2day”

4

5

+

10

9

-

“tree”

“house”

+

“you”

“r”

+

3

“D”

+

11

2
evaluates to
*

22

10

2
evaluates to
/

5

Unit 4 Lesson 1 - Activity

9

1

"treehouse"

“your”

“3D”

​

​

kit

kit

boo

kit

boo
1

2

00 var kit

01 kit ← 1

02 var boo

03 boo ← kit + 1

04 kit ← 5

kit

1

1

kit

boo
5

2

1

Note: Variables aren’t
“connected”. Changing kit
doesn’t change boo.

Unit 4 Lesson 1 - Activity

Open Ended

Run this program. What would be stored in the fuzz and clip variables?

3

4
evaluates to
+

7

5

2
evaluates to
-

3

“for”

“ever”
evaluates to
+

“forever”

“gr”

8
evaluates to
+
“gr8”

2

“day”
evaluates to
+
“2day”

4

5

+

10

9

-

“tree”

“house”

+

“you”

“r”

+

3

“D”

+

11

2
evaluates to
*

22

10

2
evaluates to
/

5

Unit 4 Lesson 1 - Activity

9

1

"treehouse"

“your”

“3D”

​

​

pow

pow

pow

●Numbers and strings are two different types of values

●Expressions evaluate to a single new value

●When variables are in the expression just make a
copy, don’t change the actual variable.

●Variables are “assigned” a new value

●Evaluate first, then assign

●Old values are deleted forever.

●Assignment just moves information around. It does
not “connect” variables.

“hi”

22

10

2
evaluates to
/

5

00 var pow

01 pow ← 1 + 2

02 pow ← 3 + 4

3

7

3

Unit 4 Lesson 1 - Activity

In some languages (including Javascript)

the assignment operator is not written as

←

it is written as

=

Unit 4 Lesson 1 - Activity

fuzz ← fuzz + 1

it is written as

fuzz = fuzz + 1

In math = means “are equal forever”

We’ll see this more next time.

Unit 4 Lesson 1 - Activity

Expression: a combination of operators and values that evaluates to a single value

Variable: holds one value at a time

Assignment Operator: allows a program to change the value represented by a variable

Unit 4 Lesson 1 - Wrap Up

01 pow ← 1 + 2

pow

3

← OR =

Multiple Choice

What will the value of score be at the end of the program?

• 1

• The score is: 4

• 4

• The score is: score

Wrap Up

• Create score variable

• score is 3

• score is 4

• score is The score is: 4