Array elements are retrieved by specifying the offset of the element you want. Since array elements are a fixed size, you can also retrieve elements using simple pointer arithmetic. In actual fact, this is the underlying mechanism used when you supply an offset.
Consider the following array declaration:
int myArray[5] = { 1, 2, 3, 4, 5 };
Memory is allocated to myArray according to the type of the element specified. The type is int, therefore each element will be exactly 4 bytes in length. The subscript [5] allocates 5 elements to this array, thus 20 bytes (5 x 4 bytes) are allocated in total.
myArray refers to the first address of the memory location where the memory was allocated. It therefore refers to the first element in the array, which is offset 0. To retrieve the value stored at offset 0 we specify the offset as a subscript:
int x = myArray[0];
This effectively copies the value 1 (the value we stored in the first element) and places it in the memory allocated to x.
If we want to copy the last element, the fifth element, we specify the final offset, which is 4.
int y = myArray[4];
As before, this copies the value 5 and places it in the memory allocated to y.
Note that to access the nth element of an array, we specify the offset n-1. Offsets are zero-based, so the last element of an n dimension array is also offset n-1.
If we use pointers, we can better understand the underlying mechanism. myArray refers to the starting address of the entire array, so we can dereference the array by allocating a pointer to this memory location.
int * p = myArray;
This copies the address of myArray and stores it in the memory allocated to p. Therefore p points at the first element in the the array and we can retrieve the value of that element by using the indirection operator.
int z = *p;
This is the same as saying z = myArray[0].
To access the next element (found at offset 1), we simply increment the pointer's value by 1.
++p;
Note that if the value in p was originally the memory location 0x00123456, it is easy to assume it must now be 0x00123457 -- a difference of 1 byte. But p was declared as a pointer to int, so we actually increment the memory address by 4 bytes. So, p now stores the address of myArray[1].
So when we retrieve the element myArray[1], what we're really doing is accessing the value stored 1 x 4 bytes away (offset) from the memory location referred to by myArray. All this is done Behind the Scenes, but is no different to allocating a pointer to myArray, incrementing it by the specified offset, and finally returning the value through indirection.
We can also use indirection to change the value of an element:
*p = 10;
This is the same as saying:
myArray[1] = 10;
The only problem to be aware of when working with pointers is that your pointer can end up pointing at memory outside of the array. However the same can be said of any pointer. Always make sure you know what you're pointing at before attempting to access the value stored at that location.
Elements of the array.
the length of the array
length
An array of 2 times 3 is a one-dimensional array of 2 elements each of which is a one-dimensional array of 3 elements. In other words, it is an array of arrays, also known as a two-dimensional array. We can imagine a two dimensional array as being a table with rows and columns. A 2 times 3 array has 2 rows and 3 columns. Each row is itself an array of 3 elements. However, we can also say that each column is an array of 2 elements.
Passing array elements to a function is achieved by passing the individual elements by reference or by value, just as you would any other variable. However, passing the entire array requires that you pass a pointer-to-pointer to the array along with the dimension(s) of the array.
An array literal is a comma-separated list of the elements of an array. An array literal can be used for initializing the elements of an array.
You cannot add elements to a fixed array in C or C++. If, however, the array is declared as a pointer to an array, you can add elements by allocating a new array, copying/adding elements as needed, reassigning the new array to the pointer, and deallocating the original array.
An ordered array is simply an array where all elements are in sorted order: int a[] = {3, 6, 9, 10, 15, 21}; // ordered array An array can either be initialised with ordered elements or the elements may be sorted after initialisation. When inserting new elements into an ordered array, the order must be maintained.
Elements of the array.
the length of the array
length
A single dimension array is an array with one dimension. It is a collection in memory of one or more elements of the same type. int array[100]; declares an array of int's of size 100 elements. The elements are referenced as array[0], the first one, through array[99], the last one.
An array.
An array of 2 times 3 is a one-dimensional array of 2 elements each of which is a one-dimensional array of 3 elements. In other words, it is an array of arrays, also known as a two-dimensional array. We can imagine a two dimensional array as being a table with rows and columns. A 2 times 3 array has 2 rows and 3 columns. Each row is itself an array of 3 elements. However, we can also say that each column is an array of 2 elements.
Passing array elements to a function is achieved by passing the individual elements by reference or by value, just as you would any other variable. However, passing the entire array requires that you pass a pointer-to-pointer to the array along with the dimension(s) of the array.
Ah, honey, in C, you can get the number of elements in an array by dividing the total size of the array by the size of one element. So, if you have an array of integers, you can do something like int size = sizeof(array) / sizeof(array[0]); and voilà, you've got the number of elements. Just be careful with those pesky pointers and make sure you're not trying to count elements in a pointer instead of an actual array.
An array is a collection of related data elements of same type.Structure can have elements of different types.An array is a derived data type.A structure is a programmer-defined data type.A struct can contain multiple data types, whereas an array can not.