ARRAY

Introduction And Definition

* An array in C/C++ is a "collection of related data elements of the same type that are referenced by a common name or is a variable which can store multiple value at a same time of same data types.". Generally, it is just another data type, aggregate data type or derived data type.

* All the elements of an array occupy a set of contiguous memory locations and by using an index or subscript we can identify each element.

* For example, instead of declaring mark1, mark2, ..., markN to store and manipulate a set of marks obtained by the students in certain courses, we could declare a single array variable named mark and use an index, such as j, to refer to each element in mark. This absolutely has simplified our declaration of the variables.
 
* Hence, would refer to the element in the array mark. Thus by changing the value of j, we could refer to any element in the array, so it simplifies our declaration.

*  For example, if we have 100 list of marks of integer type, we will declare it as follows:

                int mark1, mark2, mark3, ... , mark100;

If we have 100 marks to be stored, you can imagine how long we have to write the declaration part by using normal variable declaration?

*  By using an array, we just declare like this:

int mark[100];

This will reserve 100 contiguous/sequential memory locations for storing the integer data type.

Graphically can be depicted as follows:



Array can divided on the following categories :

One Dimensional Array :

Declaration:  
                            Dimension refers to the array size that is how big the array is. A single dimensional array declaration has the following form:

array_element_data_type array_name[array_size];

Here, array_element_data_type declares the base type of the array, which is the type of each element in the array. array_size defines how many elements the array will hold. array_name is any valid C/C++ identifier name that obeys the same rule for the identifier naming.
For example, to declare an array of 20 characters, named character, we could use:

char character[20];

Can be depicted as follows:



In this statement, the array character can store up to 20 characters with the first character occupying location character[0] and the last character occupying character[19].

Note:- The index runs from 0 to 19. In C/C++, an index always starts from 0 and ends with (array size-1). So,notice the difference between the arraysize and subscript terms.

Examples of the one-dimensional array declarations:

int x[20], y[50];


float price[10], yield;


char letter[70];

* The first example declares two arrays named x and y of type int. Array x can store up to 20 integer numbers while y can store up to 50 numbers. 
* The second line declares the array price of type float. It can store up to 10 floating-point values.  
* The third one declares the array letter of type char. It can store a string up to 69 characters. (Why 69? Remember, a string has a null character (\0) at the end, so we must reserve for it.)

Just like ordinary variables, arrays of the same data type can be declared on the same line. They can also be mixed with ordinary variables of the same data type like in the second line together with yield.

Initialization:
                               An array may be initialized at the time of its declaration, which means to give initial values to an array.

Initialization of an array may takes the following form:

For examples:

int id[7] = {1, 2, 3, 4, 5, 6, 7};

float x[5] = {5.6, 5.7, 5.8, 5.9, 6.1};

char vowel[6] = {‘a’, ‘e’, ‘i’, ‘o’, ‘u’, ‘\0’};

* The first line declares an integer array id and it immediately assigns the values 1, 2, 3, ..., 7 to id[0], id[1], id[2],..., id[6].
* In the second line assigns the values 5.6 to x[0], 5.7 to x[1], and so on. 
* Similarly the third line assigns the characters ‘a’ to vowel[0], ‘e’ to vowel[1], and so on.

Note :- For characters we must use the single apostrophe (’) to enclose them. Also, the last character in the array vowel is the NULL character (‘\0’).

Initialization of an array of type char for holding strings may takes the following form:

char array_name[size] = "string_lateral_constant";

For example, the array vowel in the above example could have been written more compactly as follows:

char vowel[6] = "aeiou";

When the value assigned to a character array is a string (which must be enclosed in double quotes), the compiler automatically supplies the NULL character but we still have to reserve one extra place for the NULL.

Important things : 

Case 1 : If we declare an array as follow:

                      int array[7]={1,2,3};
 then                  
array[0]=1
array[1]=2
array[2]=3
& rest element assigned zero automatically i.e. array[5]=0 .

Case 2 : 
                      int array[ ]={1,2,3};
 then                  

array[0]=1
array[1]=2
array[2]=3
& rest element assigned any garbage value like array[5]=78346 .

Case 3 : Address of this array is differ by 4 in 32 bit compiler
i.e.
     Address of array[0] is 0x8641 then address of array[1] is 0x8645.
         

Array And Function: Passing One Dimensional Arrays To Function :

   A function can receive the address of an array by using:
              
           (1) A pointer.

           (2) A sized array (dimension is explicitly stated), e.g. s[20] or

           (3) An unsized  array (dimension is not stated), e.g. p[ ].

For example, to receive an array named x of type float in functions, we may declare any one of the following:

           // Pointers, will be explained in another Module

           int myfunction(float *x)

           // Sized array

           char yourfunction(float x[5]);

           // Unsized array

           void ourfunction(float x[])

  But you will see later, the second and third methods not used in practice.

  The following program segment illustrates the passing of an array address to a function using a pointer.
  Here, the memory address of x is passed to the parameter pter, a pointer. Remember this; an array name (without the size) is the pointer to the first array’s element. We will discuss this in more detail later.

           // function prototype
           void func(float *);
           int main()

           {
                     float x[5];
                     // an array name (without the bracket) is
                     // the pointer to the first array element
                    func(x);
                     return 0;
           }

           // function definition
           void func(float *pter)
           { 
                     return;
           }
 

Accessing Array’s Element :

                                                              The following program example declares and initializes the array named y of type int. It uses a for loop with index i to access the successive elements in y. For each loop iteration, the value accessed is added to the variable total, which is finally displayed. Note that the loop index i run from 0 to 6,
not 1 to 7.
 

geditor window

 Output : 

terminal output window 

 Now let us see another illustration to print array element :

geditor window

Output :

 terminal output window

Searching For A Value :

                                                       To search an array for a value, you can use a for loop within the if statement. In other words, the program looks at each element in the array and checks if it matches the given value in the if expression.

 The following example, finds the smallest element in the array named arr. First, it assumes that the smallest value is in arr[0] and assigns it to the variable min.Then it compares min with the rest of the values in arr, one at a time. 

Output :

Exchanging Values of Variables : 

                                                                         It is sometimes necessary to shuffle the order of the elements of an array. Sorting arrays calls for the values of some elements to be exchanged. It would therefore be helpful to first learn the technique of swapping variables. How would you swap the values of the variables, let say, num1 and num2 (that is exchanging the value of num1 in num2)?
 You must use a third variable as in the following example:

//assign num1 to third_var 
third_var = num1; 
//then assigns num2 to num1 
num1 = num2; 
//finally assigns third_var to num2 
num2 = third_var;

 The process can be illustrated as shown below.

Sorting Variables :

                             Sorting is defined as arranging data in a certain order, is a very common activity in data processing.
Many algorithms (techniques) are available to perform sorting.We will discuss the sorting in details later.

geditor window

Output :

 terminal output window

Two Dimensional Array :

Declaration: 

A two dimensional array has two subscripts/indexes. The first subscript refers to the row, and the second, to the column. Its declaration has the following form:

  data_type array_name[1st dimension size][2nd dimension size];

 

For examples:

       int x[3][4];

       float matrix[20][25];

The first line declares x as an integer array with 3 rows and 4 columns and the second line declares a matrix as a floating-point array with 20 rows and 25 columns.

Descriptively, int x[3][4] can be depicted as follows: 

We can see that for [3][4] two-dimension array size; the total array size (the total array elements) is equal to 12. 

Hence for n rows and m columns, the total size equal to mn.

* The item list is read starting from the first row from left to right, and then goes to the next row and so on.

* A set of string s can be stored in a two-dimensional character array with the left index specifying the number of strings and the right index specifying the maximum length of each string.
 

* For example, to store a list of 3 names with a maximum length of 10 characters in each name, we can declare:

char name[4][10];

                 //can store 4 names, each is 10 characters long

Initialization:

Just like the one-dimensional array, a two dimensional array can also be initialized. 

For example, the previous first array declaration can be rewritten along with initial assignments in any of the following ways:

int x[3][4] = {1,2,3,4,5,6,7,8,9,10,11,12};

Or

The results of the initial assignments in both cases are as follows:

     x[0][0]=1                  x[0][1]=2             x[0][2]=3      x[0][3]=4
     x[1][0]=5                  x[1][1]=6             x[1][2]=7      x[1][3]=8
     x[2][0]=9                  x[2][1]=10           x[2][2]=11    x[2][3]=12
 

Notice the same subscript for the rows and columns; it is in the diagonal line.

You can show how the rows are filled during its initialization. For example, the array named x can be declared as follows:

                 int x[3][4] = {{1,2,3,4},{5,6,7,8},{9,10,11,12}}; 

- If the number of values given is insufficient to fill in the whole array, an initial value of zero will be assigned to all those locations, which are not given initial values explicitly.
- For example:

 

 So, an initial value of zero will be assigned to x[2][2] and x[2][3]. Similarly, in declaration:

 

An initial value of zero will be assigned to x[0][3], x[1][3] and x[2][3]. You can fill the whole array with zeroes by using:

      int x[3][4]={0};             //all array elements will be 0

In memory, despite their table-form arrangement, the elements of a two-dimensional array are stored sequentially, that mean one after another contiguously.
An array of string can also be initialized. For example, in the following declaration:

      char name[4][10] = {"Sally","Joyce", "Lisa", "Alice"};

- The values assigned are as follows:

      name[0] = "Sally"                     name[1] = "Joyce"
      name[2] = "Lisa"                      name[3] = "Alice"
 

- Note that the second subscript here is unnecessary and therefore omitted.

Two-Dimensional Array Manipulation :

 The following example prints the 3 x 3 array’s subscript and their element.

 

Output :

 

The following program example illustrates the use of two-dimensional arrays. This program calculates the average of all the elements in the integer array named x. The program uses two nested for loops.

The outer loop with index i provides the row subscript. The nested for loops therefore accesses each element of the array and the inner loop with index j provides the column subscript.

Output :

 

The following program example illustrates the use of three nested for loops. The program multiplies matrix x and y and stores the resulting matrix product xy in matrix z. Both x and y must be compatible for multiplication that means, the number of columns of x must be equal to the number of rows of y.

 

Output :

 

 Multidimensional Arrays :

When an array has more than one dimension, we call it a multidimensional array. 

We have already looked at multidimensional arrays with two dimensions. The declaration and manipulation of other multidimensional arrays in C/C++ are quite similar to that of the two dimensional array.

The declaration takes the following form:

 
                      Data_type name[size1][size2]...[sizeN];

 
  -    For example:

 int y[4][5][3];

    Declares a 3-dimensional array with a depth of 4, 5 rows and 3 columns. 

The are no limitation on the dimension of the arrays, but the dimension more than two dimensional arrays are rarely used because of the complexity and code readability.

 More example on array click here