This shows that when one of the operands is of the float data type, floating point math is used for the entire calculation and, as a result, suffers from the usual drawbacks of large memory size and slow operation. In this most recent example, the variable C was of the float data type and as a result could store the fractional value. Rather than giving you a compiler error for something you should not be able to do, the Arduino compiler will instead spit out some rather odd and unexpected numbers.
These can be used to either increment, raise the value, or decrement, lower the value, using just one operator.
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In this case, the variable myValue now contains the numerical value 1. Likewise, we can decrement the value using the -- character symbol, as follows: myValue--; Here, myValue now contains 0 again. In this way we can change either of the initial values for these two variables at the beginning of the code without needing to hunt down each line in the sketch.
Compound operators are also useful for counters and indices and especially help compact the code into a more readable form when we get to the for loop control structures later. When we consult the order of operations, however, we find that multiplication always takes precedence over addition regardless of the order they appear in the expression; so the correct answer would be In this case, parenthesis take precedence over every other operator, so 5 is added to 10 and that sum is then multiplied by 3 for the modified result of Parenthesis may also be added to an expression not necessarily to modify the order of operations, but rather just to make things easier to understand.
Here, the sum of 5 and 5 is then multiplied by 5 for a total value of Table shows the normal order of operations ranked by highest precedence at the top and lowest at the bottom. We have covered some of these operators in this chapter, while others will be discussed later. Also remember that the operators we discussed in this chapter can be used to increment, decrement, or perform other arithmetic and compound operations, which are performed in a specific order of operations.
In this chapter, we will put the variables to work with some fundamental structures that the Arduino uses to make decisions and perform repetitive operations. This could include reading a switch or sensor and doing something based on its input, performing one or a set of operations for a defined number of times or until a different condition is met, or performing a range of operations depending on a range of conditions. The tilt switch we are using to make this happen is a small metal tube with two wires coming out the bottom.
Inside is a small metal ball that, when flat makes contact with the two wires closing the switch, but when tilted, the ball rolls away— opening the switch.
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In this circuit, when the switch is open, a resistor connects the input pin to ground, providing a LOW signal. We will use these two states to light up our LED. Figures and show how to wire it up. Tilt Blink illustration Uploading the Source Code In our last project, we managed to cycle through seven different colors with our LED in a fairly simple and straightforward manner.
In the last example, it would take 8 seconds to make it through all of the colors once. In that amount of time we could have easily missed a switch being triggered because our code was not smart enough, or fast enough, to do two things at once. In our source code for this project, shown in Listing 41, we have attempted to solve this by speeding things up a bit, reducing our time between readings from 8 seconds to a half of a second.
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It contains the three pin numbers for our RGB LED 9, 10, 11 and each position in the array can be accessed by an index number 0, 1, 2. The variable time is used for the delay between each color—we speed it up here to make it more interesting. Finally switchPin is the pin that our tilt switch is connected to.
For example, if we start with red, then we need to add green to make yellow, and then turn off red to leave green. The next thing we need to do is to read the state of the switch to see if it has been triggered or not. To get around this, we can very quickly read the state of the digital input twice with a short pause between each reading and compare the results.
If the two readings are the same, chances are pretty good that the switch has indeed been triggered. This is called debouncing. Once the switch has been triggered, we begin the process of quickly blinking through each of the seven colors. This way newPin is always one value ahead of oldPin. From the declaration of these two variables earlier, each start at 0, oldPin stays at 0 while newPin becomes 1. These values will be used as the index in the array and correspond to pin numbers for the RGB LED, so index 0 is pin 9, index 1 is pin 10, and index 2 is pin Each time through the loop these numbers will increment by 1.
This is what will allow us to not only make the primary colors, but also the intermediate colors, as well. The one color that will not work this way is white.
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Comparative operators are used to compare the left side of an expression against the right side to produce a value of true or false. With this piece of information, the Arduino can use it to make decisions depending on the type of control structure being used. In this case, the expression would return as true if myValue contained the value 5, and false if it did not. Table lists other comparative operators that we will discuss in greater depth and provide examples for in this chapter and beyond.
In this way, you could use a logical operator, for example, to make two separate comparisons, and only do something if both comparisons are true. The final logical operator is the not! This one is a little different from the others in that it works on only one operand and returns true only if the expression is false. Take the following example:!
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Comparative and logical operators are going to play a crucial part in the Arduino decision-making process. Table provides a quick reference of the logical operators to refer back to. The Arduino microcontroller reads the lines of code in our sketches from the top of the code until it reaches the end at the bottom, and, when there are no more commands to execute, will bounce back to the top of the loop function and start over again. The order or direction in which code is executed is called program flow and the ability to alter this order of executing commands is something called flow control.
There are two kinds of statements available in Arduino C for controlling program flow: conditional statements that make decisions based on whether or not a condition is true and iterative statements that perform things a certain number of times or until a condition becomes false. Conditional statements that include the if and switch statements selectively perform certain actions based on the state of a condition.
Iterative statements that include the for and while statements are often called loops because, just like our loop function, they will loop to the beginning of the statement and repeat their code when a condition has been met. If The if statement is the simplest of the control structures and is among the most prominent method for Arduino decision making.
It will perform a block of code if a specific condition is met. If the condition is not met, in that they return the value false, then the following statement s will be ignored and are not executed. A common use for the if statement is to read the state of a digital pin and perform an action based on its condition. Notice that this is another example of a simple statement that does not require curly braces. If we wanted the LED to only turn on when the switch is activated and to remain off the rest of the time, we would use an if…else statement.
Essentially, if the condition is true, only the first statement will be executed and if it is false, only the second statement will be executed. What makes the for loop unique is that it is based on a counter, or a specific variable that is incremented each time the loop is repeated. This counter is even quite useful, as the counter itself can be used just like any other variable by statements that reside inside the loop, as you will see in later examples. Of these, the first is the counter variable declaration or initialization and is run only once the first time through the loop.
The second statement is the conditional statement using comparative operators just like those found in the if statement and is tested each time through the loop. If, however, the condition returns false, the for loop will end. The third and final statement increments the counter variable each time the enclosed block of code is executed. Sometimes it would be nice to always run the enclosed code at least once before evaluating its condition and for that we would use the do statement, or do loop. The do loop is like a modified while statement in that it executes a line or lines of code and then tests for a condition at the end of the loop rather than the beginning before deciding to loop to the beginning again or not.
When the condition is no longer true, the do loop will exit and return to normal program flow. Switch The switch statement is like a really nifty version of the if statement in that it can execute one or more blocks of code, depending on a range of conditions. Basically, the switch statement compares the value of an expression against a list of cases executing whatever code begins after that case when a match is found.
After the colon that defines the case, we can have a block of code that is executed when that case is true. The default case allows for code to be executed when a specific case has not been previously specified. If the tilt switch is activated then the pin will read as HIGH, which if you remember is basically equal to the value 1, and the code for case 1 will be executed.
If the tilt switch is not activated it will read as LOW or 0, so the code beginning with case 0 will be executed until the end of the switch statement. This will also include the code following case 1 because the normal program flow did not reach the closing curly brace yet.danardono.com.or.id/libraries/2020-02-10/fudeq-galaxy-note-9.php
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What this means is that, assuming the switch statement is the only code in our loop function, when the tilt switch is off, the LED will blink on and off every 1 second but when the tilt switch is on, the LED will stay on and not turn off again until the tilt switch is turned off. Break The break statement can be used inside other control statements to immediately end the loop or statement.
If we borrow our five-blink sample from before, we could add an if statement followed by the break statement to exit out of the loop if a switch is activated. The continue statement only works on iterative statements like the for, while, and do loops and can be used among other things to skip odd or even numbers in a for loop. You should have a basic understanding of how to make decisions using conditional statements and how to perform repetitive tasks in iterative statements, or loops.
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Of course, we will continue to work with these concepts in later discussions, building out from our foundational understanding of how we can structure Arduino sketches. But for now, that about wraps up the discussion of the generally more Cbased structural programming syntax.
From here, we will discover more of the uniquely Arduino aspects of programming the Arduino microcontroller board that specifically relate to sensing and controlling the physical world. These are the parts of the Arduino library that make Arduino C unique. This is going to be the really fun stuff. Programming a microcontroller can be rather unique because of its ability to easily turn on and off motors, lights, and other actuators, as well as read from switches and sensors.
This chapter will take as its focus the various digital input and output functions available and how to interface the needed hardware to make them work. What unifies the functions and code in this chapter as being digital is that they all have only two different states: on or off. Other forms of digital input include pushbuttons, mat switches, magnetic or reed switches, thermostats, passive infrared motion detectors, and oh so many more. We can use digital output to turn on not only LEDs but also to make sound, create movement with motors or solenoids, and even control larger devices using transistors and relays.
These are used mostly for inputs, outputs, and power. Figure shows a simple illustration of the Arduino Uno interface board. Your board might be a little different.