$$ \newcommand{\floor}[1]{\left\lfloor{#1}\right\rfloor} \newcommand{\ceil}[1]{\left\lceil{#1}\right\rceil} \renewcommand{\mod}{\,\mathrm{mod}\,} \renewcommand{\div}{\,\mathrm{div}\,} \newcommand{\metar}{\,\mathrm{m}} \newcommand{\cm}{\,\mathrm{cm}} \newcommand{\dm}{\,\mathrm{dm}} \newcommand{\litar}{\,\mathrm{l}} \newcommand{\km}{\,\mathrm{km}} \newcommand{\s}{\,\mathrm{s}} \newcommand{\h}{\,\mathrm{h}} \newcommand{\minut}{\,\mathrm{min}} \newcommand{\kmh}{\,\mathrm{\frac{km}{h}}} \newcommand{\ms}{\,\mathrm{\frac{m}{s}}} \newcommand{\mss}{\,\mathrm{\frac{m}{s^2}}} \newcommand{\mmin}{\,\mathrm{\frac{m}{min}}} \newcommand{\smin}{\,\mathrm{\frac{s}{min}}} $$

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Project Task - Middle Button

A variable stores values that we can later use in the program.

A variable can be:

  • Numerical (stores a number)

  • Logical (stores logical values true/false)

  • Textual (store text “Hello”)

A variable can be understood as a space in the computer memory, something like a box, in which, during the execution of the program, we can store some interim values. Variables have names. When we want to use the value of the variable, it is enough to use its name.

A variable is created in the following manner, in the category Variables (1), click on the button Make a variable (2) and type in the name of that variable in the field (3). By clicking the button OK (4), you have created a variable.

_images/42.png

We will demonstrate the use of variables by creating a program, which displays how many times the user pressed the middle button on the EV3 Brick.

We need to create the variable Brojac. We will set the initial value of the counter to be 0, by using the block setBrojac. We then drag this block into the block Start. Within this block, we will also show the value of the counter in the very beginning on the EV3 Brick screen by using the block show.

The look of the code:

_images/74.png

Based on the setup of the task, we need to register every time the user presses the middle button on the brick. This will be achieved by using the following block:

_images/78.png

When the pressure made to the middle button of the brick is registered, the value of the counter should increase by 1. We can do this by using the block change from the category Variable. We will use the block show to display the new value of the variable Counter.

The look of the code:

_images/75.png

The look of the final code:

_images/76.png

Connect the EV3 Brick to the computer via USB cable and download the .uf2 file to your computer by clicking the button dugme1. By dragging the file onto the EV3, it is ready to start working.

Simulation:

_images/78_.png

We can demonstrate the use of variables with another example. We can create a program, which will count how many black lines the LEGO robot has crossed.

Let’s create the variable Brojac. Using the block setBrojac, we will set the initial value to be 0. We should then drag this block into the block Start. Within this block, we will also show the value of the counter in the very beginning on the EV3 Brick screen by using the block show. We will also drag the block pravo into the given block, which will enable the robot to move continuously.

The look of the code:

_images/81_.png

Based on the setup of the task, we need the sensor to register black; this will be achieved by using the block that has the drop-down list from which we can choose the color black:

_images/25.png

When the sensor registers black, it is necessary to increase the value of the counter by 1. We can do this by using the block change from the category Variable. For displaying the new value of the variable Counter, we will use the block show.

Look of the code:

_images/82_.png

The look of the final code:

_images/812.png

Connect the EV3 Brick to the computer via USB cable and download the .uf2 file to your computer by clicking the button dugme1. By dragging the file onto the EV3, it is ready to start working.