Introduction to C Arrays

An array is a group of identically typed data elements that may be referenced by a common name. The C language does not impose any restrictions on the number of dimensions in an array, though some implementations could. A one-dimensional array is analogous to a list, a two-dimensional array is analogous to a table. When the number of dimensions is unclear or immaterial, some books refer to one-dimensional arrays as vectors, two-dimensional arrays as matrices, and use the broad word "arrays" instead. Download these FREE Ebooks:
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Setting Up Arrays

Like other variables, arrays can be initialised when they are declared. After the equals sign, provide the initialization data in curly braces. In the instances below, commas are used. You may begin an array partially by giving it fewer data items than it needs. The remaining array elements will be initially set to zero automatically. The array's dimension is not necessary for full initialization of an array. The array will be enlarged by the compiler automatically to fit the initialised data.
Examples:

Specific Initializers

There is an alternative technique in C99 that enables you to initialise some components at different times than the default. This approach can be used with conventional initialization.
For example:
int numbers[ 100 ] = { 1, 2, 3, [10] = 10, 11, 12, [60] = 50, [42] = 420 };

• The first three items in this example have beginning values of 1, 2, and 3, respectively.
• The 11th element, element 10, is then initialised to 10.
• Initial values for the next two elements, numbers 12 and 13, are 11 and 12, respectively.
• Initial values for elements 60 (the 61st) and 42 (the 43rd) are 50 and 420, respectively.
• (Take note that the prescribed initializers need not occur in any particular order.)
• All uninitialized values are initialised to zero, much like the conventional ways.
• The greatest initialised location defines the size of the array if the array size is not specified.

Utilizing Arrays

• The index (offset) of the requested element must be entered after the array name in square [] brackets in order to access an element of an array.
• Subscripts in an array must be of the integer type. (Char, int, long int, etc.)
• HIGHLY IMPORTANT In C, array indices begin at zero and go down to one less than the array's size. A five member array, for instance, will have indices 0 through 4. This is due to the fact that the index in C really represents an offset from the array's start. (The first element has zero offset because it is the first in the array.) Landmine: Forgetting that indices begin at zero and end one less than the array size is the most typical error made while working with arrays in C.
• In order to run the same computations on all (or some portion of) the data items in the array, arrays are frequently used in conjunction with loops.

Establishing Arrays

Variables in arrays are defined in the same way as variables of the same data type, with the exception that one pair of square [] brackets is added after the variable name for each array dimension. The size of the rows, columns, etc. of uninitialized arrays must be stated inside square brackets. When declaring an array in C, the dimensions used must be positive integral constants or constant expressions. Variables may be utilised in C99 as long as they have positive values at the time the array is declared and the dimensions are still required to be positive integers. (Space is only ever allocated once, at array declaration time. If the variable used to declare the array changes in the future, the array's sizes DO NOT change.)
Examples:

Arrays with several dimensions

After the variable name in the declaration statement, several sets of square [] brackets are used to declare multi-dimensional arrays. If a one-dimensional array is to be fully initialised, the dimension does not need to be specified. By analogy, if a multi-dimensional array is to be started entirely, it is not necessary to supply the first dimension. The second and subsequent dimensions must be provided in any scenario. The first dimension of two-dimensional arrays is typically thought of as the number of rows, and the second dimension as the number of columns. This convention shall be used while talking about two-dimensional arrays. In C/C++, a two-dimensional array is referred to as an array of ( single dimensional arrays ). A single dimensional array of five elements, each of which is a single dimensional array of six integers, is an example of a "int number." By extension, "int numbers[12][5][6]" would describe a collection of twelve items, each of which is a two-dimensional array, and so on. An alternative perspective is that C stores two-dimensional arrays as rows, with each row's items being stored as a single unit. Knowing this can occasionally result in more effective programmes. As with single dimensional arrays, multidimensional arrays can be fully initialised by listing every data element between a single set of curly brackets. To make the programme more understandable, it is preferable programming practise to surround each row within a different subset of curly brackets. If any row other than the final is to be partially initialised, this is necessary. The last item enclosed in braces is not followed by a comma when subsets of braces are used; instead, the subsets are separated by commas. When incomplete initialization data is provided, multidimensional arrays may only be partially initialised. If subset brackets are used, individual rows of a multidimensional array may be partly initialised. A multidimensional array's individual data elements can be accessed by completely qualifying an array element. Alternately, by partly qualifying the array name, a reduced dimensional array may be accessed. For instance, data[1][2][5] would refer to a float, data[1][2] to a one-dimensional array of floats, and data[1] to a two-dimensional array of floats if "data" had been specified as a three-dimensional array of floats. The motivation behind doing this and the reasons why are related to memory-management concerns outside the purview of these notes.

Character Strings as Character Arrays

• The "string" class type, which did not exist in conventional C, is a novel addition to C++.
• Traditionally, character arrays have been used to manage character strings.
• As a terminator signal, a null byte (character constant zero, '0') is used to indicate the string's end.
• Ordinary quoted texts, such as "Please enter a number >," are saved as arrays of characters with null ends.
• There are several functions for working with conventional character arrays in the cstring package.
• Using conventional character arrays in the C manner, C++ string objects may be initialised:
• "Please enter your choice >" is the string prompt;

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