Arrays - C++ Tutorials. An array is a series of elements of the same type placed in contiguous memory locations that can be individually referenced by adding an index to a unique identifier. That means that, for example, five values of type int can be declared as an array without having to declare 5 different variables (each with its own identifier). Instead, using an array, the five int values are stored in contiguous memory locations, and all five can be accessed using the same identifier, with the proper index. For example, an array containing 5 integer values of type int called foo could be represented as: where each blank panel represents an element of the array.
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In this case, these are values of type int. These elements are numbered from 0 to 4, being 0 the first and 4 the last; In C++, the first element in an array is always numbered with a zero (not a one), no matter its length. Like a regular variable, an array must be declared before it is used. A typical declaration for an array in C++ is.
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This means that none of its elements are set to any particular value; their contents are undetermined at the point the array is declared. But the elements in an array can be explicitly initialized to specific values when it is declared, by enclosing those initial values in braces . For example: int foo . For example, in the example above, foo was declared having 5 elements (as specified by the number enclosed in square brackets, .
If declared with less, the remaining elements are set to their default values (which for fundamental types, means they are filled with zeroes). For example: int bar .
In this case, the compiler will assume automatically a size for the array that matches the number of values included between the braces . Therefore, there is no longer need for the equal sign between the declaration and the initializer. Both these statements are equivalent: 1.
If no explicit initializer is specified, all the elements are default- initialized (with zeroes, for fundamental types). Accessing the values of an array. The values of any of the elements in an array can be accessed just like the value of a regular variable of the same type. By this same reason, its last element is foo. Therefore, if we write foo. This can create problems, since accessing out- of- range elements do not cause errors on compilation, but can cause errors on runtime.
The reason for this being allowed will be seen in a later chapter when pointers are introduced. At this point, it is important to be able to clearly distinguish between the two uses that brackets . They perform two different tasks: one is to specify the size of arrays when they are declared; and the second one is to specify indices for concrete array elements when they are accessed. Do not confuse these two possible uses of brackets . For example, a bidimensional array can be imagined as a two- dimensional table made of elements, all of them of a same uniform data type. The C++ syntax for this is: and, for example, the way to reference the second element vertically and fourth horizontally in an expression would be: (remember that array indices always begin with zero).
Multidimensional arrays are not limited to two indices (i. They can contain as many indices as needed. Although be careful: the amount of memory needed for an array increases exponentially with each dimension. For example: char century . This amounts to more than 3 billion char!
So this declaration would consume more than 3 gigabytes of memory! At the end, multidimensional arrays are just an abstraction for programmers, since the same results can be achieved with a simple array, by multiplying its indices: 1. The following two pieces of code produce the exact same result, but one uses a bidimensional array while the other uses a simple array: multidimensional arraypseudo- multidimensional array#define WIDTH 5.
HEIGHT 3. int jimmy . This gives the code a better readability, and allows changes in the code to be made easily in one place. Arrays as parameters.
At some point, we may need to pass an array to a function as a parameter. In C++, it is not possible to pass the entire block of memory represented by an array to a function directly as an argument.
But what can be passed instead is its address. In practice, this has almost the same effect, and it is a much faster and more efficient operation. To accept an array as parameter for a function, the parameters can be declared as the array type, but with empty brackets, omitting the actual size of the array. For example: void procedure (int arg. In order to pass to this function an array declared as: it would be enough to write a call like this: Here you have a complete example: 1.
For that reason, we have included a second parameter that tells the function the length of each array that we pass to it as its first parameter. This allows the for loop that prints out the array to know the range to iterate in the array passed, without going out of range. In a function declaration, it is also possible to include multidimensional arrays. The format for a tridimensional array parameter is: base. This is necessary in order for the compiler to be able to determine the depth of each additional dimension.
In a way, passing an array as argument always loses a dimension. The reason behind is that, for historical reasons, arrays cannot be directly copied, and thus what is really passed is a pointer. This is a common source of errors for novice programmers. Although a clear understanding of pointers, explained in a coming chapter, helps a lot.
Library arrays. The arrays explained above are directly implemented as a language feature, inherited from the C language. They are a great feature, but by restricting its copy and easily decay into pointers, they probably suffer from an excess of optimization. To overcome some of these issues with language built- in arrays, C++ provides an alternative array type as a standard container. It is a type template (a class template, in fact) defined in header < array>. Containers are a library feature that falls out of the scope of this tutorial, and thus the class will not be explained in detail here. Suffice it to say that they operate in a similar way to built- in arrays, except that they allow being copied (an actually expensive operation that copies the entire block of memory, and thus to use with care) and decay into pointers only when explicitly told to do so (by means of its member data).
Just as an example, these are two versions of the same example using the language built- in array described in this chapter, and the container in the library: language built- in arraycontainer library array#include < iostream>. Other than that, the main differences lay on the declaration of the array, and the inclusion of an additional header for the library array. Notice also how it is easy to access the size of the library array.