Flags

Upload the flags program.

Now, pressing the button on pin 10 will cycle through a sequence of colors. Note the order of the sequence on a piece of paper.

Pressing the button on pin 7 will cycle through the same sequence backwards. Verify this.

Pressing the button on pin 8 will reset the RGB LED to dark.

Note that all three buttons are working as switches.

Let’s look at the program. There is one new line before setup():

int flag = 0;

The flag variable (here being set initially to ‘0’) will be used to keep track of which color is currently being lit. It is a way to give the program some memory.

The setup() function is identical to the one in the rgb-switches program.

The loop() function is using two new functions:

changeback();

Do you see how they are being used? See further down the program for what these functions are doing.

The changenext() function contains the following lines:

if (flag == 0) {flag = 1; makered(); } else if (flag == 1) {flag = 2; makegreen(); } else if (flag == 2) {flag = 3; makeblue(); } else if (flag == 3) {flag = 4; makepurple(); } else if (flag == 4) {flag = 1; makered(); }

This is a new way to use the if-else structure, to check for multiple conditions. These lines are checking what the flag variable’s value is, and then setting it to the next one in sequence, as well as changing the color.

Compare the functions changenext() and changeback(). Do you see the difference?

Try the following (save as flags-mod in your Mod folder first!):

1. Change the sequence of colors to green, purple, blue, red. Make this change in both changenext() and changeback() functions.
2. Use the new functions that you defined for other colors in the previous program (put them in this program as well), and make the color sequence longer. The flag variable will need to take larger values for this.

CHECKPOINT!

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