C++: Arrays

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Arrays, in C++, are simply arrangements of 'objects' -- in the basic usage we'll be using in this tutorial, we will be using arrays to simply store lists of data (of a certain data-type). You can think of basic arrays, such as the ones we will be using in this tutorial, like tables with only one or two row(s) but multiple columns. I say "one or two rows" because each piece of data stored (whether it be an integer, string, or something entirely different) has a number assigned to it that it can be referenced by. This is called the index, and the index number simply counts up from 0 as the array gets bigger - so the first element in the array would have the index of 0, the second the index of 1, etc.

How I visualize arrays. This example is an array with some integer data.

Obviously storing data in this tabular-like manor is very useful in real world applications - a classic example that is usually given is pupils' scores in a test. Perhaps each student got a score out of 100 for their test - this data would be best stored in an integer array. In the real world the scores would probably be recorded in a text file or something similar, but we could always build in functionality to read this file and then store that data in an array inside our application.

Arrays can be created in C++ very much like "normal variables" (with a data-type followed by a name), but square brackets should be present after the array name to indicate that what you are creating is in fact an array and not just a variable. Arrays must have a set size when being declared (maybe ours would have one entry for each of the 30 students in the class), and this can be specified inside of the square brackets. Taking all of this into account, we could declare an integer array in which 30 entries can be made, with the following:

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int ClassScores[30];

It's important to remember that the index number is counted from 0, so if we were to try to visualize this array it would have index numbers from 0 to 29. We can proceed to initialize the various elements in the array by writing the array name (in this case, "ClassScores") , followed by the index number of the element we wish to target in square brackets, followed by an equals sign and then the value we wish to set it to (and then obviously a semi-colon to end the line). So if we wanted to initialize the first element (of index 0) in our array to the value '15', we could write the following:

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ClassScores[0] = 15;

The same could also be done for the scores of the other members of the class (elements of the array from index 0 to index 29). If we then wanted to use these values later (for example if we wanted to cout one or all of the elements), we can access a certain element of the array just as we did when we were assigning values to each element - by writing the array name and then the index number in square brackets. So we could output the first element in the array (remember, this is the one with the index of 0!) by writing something like cout << ClassScores[0];.

You may have noticed when we learnt how to initialize the elements in arrays earlier, that the process was extremely long and drawn out (imagine having to initialize hundreds of array elements!) - luckily there is an easier way to initialize the elements in an array. Instead of individually setting each element to a certain value (which can be done at any point in the program, not just at element initialization) we can actually initialize the elements when we declare the array! This method of initialization is accomplished by simply shoving an equals sign after the declaration of the array and then specifying the different array elements, with commas separating them, in curly brackets. This method doesn't require any value in the square brackets either as the compiler can calculate how many elements we are initializing and set the array size to that! To show this method of initialization, let's just set some values for each score in the class at the array declaration - let's cut it down to 20 this time for the sake of simplicity:

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int ClassScores[] = { 15, 30, 55, 62, 45, 63, 12, 7, 80, 98, 11, 90, 17, 57, 12, 70, 20, 32, 66, 20 };

With an array declared and initialized, we can do a whole bunch of stuff with it! A nice example might be outputting all of the students' scores - unfortunately, however, there's no really easy and clean way to do this without knowing about 'loops' or some other fancy things, so for now we'll have to just repeat a bunch of code. Generally speaking when you feel your repeating a lot of code when C++ programming, there is probably a better way to accomplish what you're trying to do, but for now just go with it. I've cut the array down to 5 elements this time, simply because I don't want to have to copy and paste a single line 20 times - you'll learn about a more elegant solution to our problem of outputting array elements in the next tutorial.

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#include <iostream> //For 'cout'

using namespace std;

int main()
{
	int ClassScores[] = { 15, 30, 55, 62, 45 }; //Declare and initialize our 'ClassScores' array
	
	cout << "1: "<< ClassScores[0] << endl;
	cout << "2: "<< ClassScores[1] << endl;
	cout << "3: "<< ClassScores[2] << endl;
	cout << "4: "<< ClassScores[3] << endl;
	cout << "5: "<< ClassScores[4] << endl;

	return 0;
}

Another really cool thing that you could do with arrays is trying to "re-create" the 'string' data-type. Before strings were widely used, people used arrays of chars - so instead of a string like "Hello", character arrays like 'H', 'e', 'l', 'l', 'o' were used -- character arrays of this kind can, unlike most, actually be outputted just by couting their name because they're so much like strings. It's worth nothing that when creating character arrays like these, however, you should also add another character onto the array, which is a "null character" which shows where the string ends - this is called the null termination of a string, and the null character is expressed via '\0'.

'Real' strings can actually be treated just like character arrays in some circumstances too - using square brackets and an index number gets a certain character of the string (for example string_name[1] of "Hello" would be 'e'). If you're feeling up to the challenge, try moving a string variable defined in code (of a fixed length) like string one = "Hello";, to a 'char' array of the same length using the information above. It probably seems a bit pointless, I know, but it's good practice with using arrays. If you don't feel up to the challenge, the code for doing such a thing (which once again would be a bit cleaner with 'loops'), is as follows:

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string one = "Hello";
char one_as_an_array[6]; //{'', '', '', '', '', ''}

one_as_an_array[0] = one[0]; //=> {'H', '', '', '', ''}
one_as_an_array[1] = one[1]; //=> {'H', 'e', '', '', ''}
one_as_an_array[2] = one[2]; //=> {'H', 'e', 'l', '', ''}
one_as_an_array[3] = one[3]; //=> {'H', 'e', 'l', 'l', ''}
one_as_an_array[4] = one[4]; //=> {'H', 'e', 'l', 'l', 'o'}
one_as_an_array[5] = '\0';   //=> {'H', 'e', 'l', 'l', 'o', '\0'}

cout << one_as_an_array << endl; //'cout' our array - only do this with 'char' arrays