ARDUINO LESSON 5: WORKING WITH STRINGS

In this lesson we will learn more about working with stings. A string is literally a string or sequence of characters. The word “Hello” is a string of characters. Stings allow your computer program to interact with the world in a way that the world understands, so it is important for us to learn a little more about strings.

In this lesson we will be using the same circuit we developed in Arduino Lesson 3.  If you need help setting the circuit up, please visit lesson 3. Hopefully you still have the circuit set up, as we have used it for the last two lessons. The circuit schematic and code we have been working with is presented below.

This circuit will allow you to independently control two Light Emitting Diodes from the arduino microcontroller

This is the code that will run this circuit.

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int redLEDPin=9; //Declare redLEDPin an int, and set to pin 9 int yellowLEDPin=10; //Declare yellowLEDPin an int, and set to pin 10 int redOnTime=250; //Declare redOnTime an int, and set to 250 mseconds int redOffTime=250; //Declare redOffTime an int, and set to 250 int yellowOnTime=250; //Declare yellowOnTime an int, and set to 250 int yellowOffTime=250; //Declare yellowOffTime an int, and set to 250 int numYellowBlinks=5; //Number of times to blink yellow LED int numRedBlinks=5;  //Number of times to blink red LED void setup() {   Serial.begin(115200);   pinMode(redLEDPin, OUTPUT);  // Tell Arduino that redLEDPin is an output pin   pinMode(yellowLEDPin, OUTPUT);  //Tell Arduino that yellowLEDPin is an output pin } void loop() { Serial.println("The Red LED is Blinking");   for (int j=1; j<=numRedBlinks; j=j+1) {     // Start our for loop     Serial.print("   You are on Blink #: ");     Serial.println(j);     digitalWrite(redLEDPin,HIGH); //Turn red LED on     delay(redOnTime);             //Leave on for redOnTime     digitalWrite(redLEDPin,LOW);  //Turn red LED off     delay(redOffTime);            //Leave off for redOffTime } Serial.println(" "); Serial.println("The Yellow Yellow is Blinking");   for (int j=1; j<=numYellowBlinks; j=j+1) {     // Start our for loop     Serial.print("   You are on Blink #: ");     Serial.println(j);     digitalWrite(yellowLEDPin,HIGH); //Turn yellow LED on     delay(yellowOnTime);             //Leave on for yellowOnTime     digitalWrite(yellowLEDPin,LOW);  //Turn yellow LED off     delay(yellowOffTime);            //Leave off for yellowOffTime } Serial.println(" "); }

In the code above, notice that we are using stings in some of our print statements. For example the line of code above the for loop for blinking the red LED reads as:

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1	Serial.println("The Red LED is Blinking");

The text in quotes is your string, and in this case is “The Red LED is Blinking”.  As you can see a string is just a string of characters. We can use strings to present meaningful words and thoughts to the user.  We are not limited to just using strings as we have above,  but we can actually create variables to hold strings. For example, in the code above one of the strings we print for the user to see is “The Red LED is Blinking”. It would be possible for us to create a variable called redMessage, and set redMessage to “The Red LED is Blinking”. In order to do this, we would need to declare the variable redMessage a string. We can do that up at the top of the program before the void setup, which would make it a global variable. The code would look like this:

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1 2	String redMessage="The Red LED is Blinking"; String yellowMessage="The Yellow LED is Blinking";

With this code we declare two new variables of type String. In addition to declaring the variables we initialize them to their respective values. By doing this we can modify our print statements in the original code to print the Strings by printing the variables we have assigned them to.

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1	Serial.println("The Red LED is Blinking");

can be replaced with

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1	Serial.println(redMessage);

Notice when we print the variable, we do not use quotes around it. When we say to print redMessage, it will print the string that was assigned to redMessage.

By assigning strings to variables instead of using them directly it makes it much easier to modify and use your code. Try and get in the habit of assigning strings to variables.

When we have string variables, it is possible to concatenate, or combine stings together.

For example, lets say we declare and initialize two variables:

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String st1="Hello"; //Create a Strign st1 and set to "Hello " String st2="World"; //Create a String st2 and set to "World" String st3;         //Declare a String st3 but dont assign value to it yet. // Now In your void loop add this st3=st1+st2;      //Combine st1 and st2 into a new variable st3 Serial.println(st3); // Print out st3

It is a good practice to try to assign strings to variables and then use the variables.

This post originally appeared here