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Arrays, Strings and Random Numbers

Arrays, strings and generating random numbers are all programming concepts which will be handy to learn about and implement in our projects.

Arrays​

An array is essentially a collection of variables stored under one name. Arrays allow us to store multiple values of the same datatype without having to create a separate variable for each value.

Declaring arrays​

We can declare an array using the following syntax:

int myNums[4] = {15, 39, 23, 47}
  • int - the members of the array are of data type int.
  • myNums - the name of the array.
  • [4] - the array will have a length of 4.
  • {15, 39, 23, 47} - the values that are stored in the array.

Accessing arrays​

We can access and manipulate values in an array by using its index (position in the array). When programming in Arduino, we must understand that arrays start counting from 0 - they are zero indexed. Therefore:

Serial.println(myNums[0]); // Prints the first value: 15
Serial.println(myNums[3]); // Prints the fourth value: 47
tip

If we try and access an index that doesn't exist in the array, for example, myNums[4], we will be faced with errors.

Looping through an array​

We can use a for loop to iterate through an array - a useful skill when working with arrays.

for (int i = 0; i < 4; i++) {
  Serial.println(myNums[i]); // prints each value in the array one by one
}

Strings​

A string is simply a sequence of characters. In fact, a string is an array of characters. We can work with strings to store and manipulate text.

String myGreeting = "Hello World";

char firstChar = myGreeting[0]; // 'H'
myGreeting[6] = 'w'; // changes 'W' to 'w'

String functions​

Strings have built-in functions to manipulate text. You can learn about many string functions here. For instance:

myGreeting.toUpperCase(); // converts to uppercase
myGreeting.toLowerCase(); // converts to lowercase
Serial.println(myGreeting.length()); // prints number of characters

Random numbers​

Random numbers allow us to bring variation into our projects by generating, well, random numbers. We can generate a random number within a given range using random():

int num = random(5, 15); // Returns 5-14

Unfortunately, it isn't that easy. By default, Arduino generates the same random numbers each time. To avoid this, we seed the generator using randomSeed(), making it generate a random number every time.

randomSeed() works by specifying a floating pin in order to return a fluctuating, unpredictable value.

randomSeed(analogRead(A0));
Example

Therefore, we can write a simple program to print out a random number between 0 and 99.

void setup() {
  randomSeed(analogRead(A0));  // Use floating pin A0
}

void loop() {
  Serial.println(random(100)); // Prints a random number from 0–99
  delay(500);
}

Assignment​

Your Turn
  1. Create an array with 5 integers. Loop through this array to work out the mean / average of these integers. Print this to the serial monitor.

Next Steps​

This section includes links to help you dive deeper into the topics from this lesson. It's optional, so don't worry if you choose to skip it.