> For the complete documentation index, see [llms.txt](https://docs.kidscode.co.za/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.kidscode.co.za/microbit-beginners/lesson-4/calculator.md).
# 1 + 1 = 2
{% hint style="info" %}
## Teachers Notes
In this lesson, the kids will learn how to assign variable to each button and perform an addition function.
* Assign a variable to button A
* Assign a variable to button B
* Value for each variable will be assigned based on number of taps on the particular button
* When A+B is pressed, the LED's will show the sum of values of variables A and B
* Shaking the micro:bit will reset the variables
{% endhint %}
## Create your new program
Click on the ***micro:bit*** icon on your toolbar or go to on your browser.
Click on "***New Project***". The MakeCode editor will appear
Delete the **forever** blocks by dragging it to the toolbar. Click on **Variables** option from the toolbar
Click **Make a Variable** and give it a name **"A"**
Click **Ok**. The variable A will now be created
Follow the same steps again to create variable "B"
Now you will have to initialize variables on start. Drag **set variable to 0 option** to the **on start** block. Select the dropdown and select variable A. Similarly pefrorm the same step for variable B.
Now we have initialized the variable. We will have to now make code for the variable to assign values based on number of taps we perform on a button. If we press button A the variable A should increase value by 1
To perform this function, drag **on button A pressed** option from **Input** toolbar. From the **Variables** toolbar, drag **change A by** option and change the value to **1**.
Repeat the same step for button B
Now we must perform the addition function when button A and B are pressed together. Drag the **on button A+B pressed** option from the **Input** toolbar
Drag show string option from the Basic Toolbar
Now we will have to perform a mathematical calculation of the variables. Open the **Math** toolbar and drag **0 + 0 option** to the code editor
Now replace the zeros with variables A and B by dragging **A** and **B** from the **Variables** toolbar
Now you must be able to reset the calculator after addition function is completed. We can reset the variables as we shake the micro:bit. To perform this function drag **on shake** option from **Input** toolbar. Add **set A to 0** and **set B to 0** options to on shake from **Variables** toolbar
## Save, download and run your code
Save you code as **Calculator** and press save to download.
Drag your code file named microbit-1-2-3.hex to the MICROBIT(D:) folder to upload your code to your micro:bit.
Test your micro:bit by pressing Button A once, then Button B once then both button A and button B at the same time. Your micro:bit will add 1 + 1 and display value 2
---
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