Introduction to Arrays in C

Introduction to Arrays in C

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  For more Https://www.ThesisScientist.com Unit6 Arrays Introduction to Arrays An array is a group of data items of same data type that share a common name. Ordinary variables are capable of holding only one value at a time. If we want to store more than one value at a time in a single variable, we use arrays. An array is a collective name given to a group of similar variables. Each member in the group is referred to by its position in the group. Arrays are alloted the memory in a strictly contiguous fashion. The simplest array is one dimensional array which is a list of variables of same data type. An array of one dimensional arrays is called a two dimensional array. One Dimensional Array A list of items can be given one variable name using only one subscript and such a variable is called a one dimensional array. e.g.: If we want to store a set of five numbers by an array variable number. Then it will be accomplished in the following way: int number [5]; This declaration will reserve five contiguous memory locations as shown below: Number [0] Number [1] Number [2] Number [3] Number [4] As C performs no bounds checking, care should be taken to ensure that the array indices are within the declared limits. Also, indexing in C begins from 0 and not from 1. Array Declaration Arrays are defined in the same manner as ordinary variables, except that each array name must be accompanied by the size specification. The general form of array declaration is: data-type array-name [size];
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  data-type specifies thetype of array, size is a positive integer number or symbolic constant that indicates the maximum number of elements that can be stored in the array. e.g.: float height [50]; This declaration declares an array named height containing 50 elements of type float. NOTE The compiler will interpret first element as height [0]. As in C, the array elements are induced for 0 to [size-1]. Array Initialization The elements of an array can be initialized in the same way as the ordinary variables, when they are declared. Given below are some examples which show how the arrays are initialized. static int num [6] = {2, 4, 5, 45, 12}; static int n [ ] = {2, 4, 5, 45, 12}; static float press [ ] = {12.5, 32.4, -23.7, -11.3}; In these examples note the following points: (a) Till the array elements are not given any specific values, they contain garbage value. (b) If the array is initialized where it is declared, its storage class must be either static or extern. If the storage class is static, all the elements are initialized by 0. (c) If the array is initialized where it is declared, mentioning the dimension of the array is optional. Accessing Elements of an Array Once an array is declared, individual elements of the array are referred using subscript or index number. This number specifies the element's position in the array. All the elements of the array are numbered starting from 0. Thus number [5] is actually the sixth element of an array. Entering Data into an Array It can be explained by the following examples: main( ) { int num [6]; int count; for (count = 0; count < 6; count ++) { printf ("n Enter %d element:" count+1); scanf ("%d", &num [count]); } } In this example, using the for loop, the process of asking and receiving the marks is accomplished. When count has the value zero, the scanf( ) statement will cause the value to be stored at num [0]. This process continues until count has the value greater than 5. Reading Data from an Array Consider the program given above. It has entered 6 values in the array num. Now to read values from this array, we will again use for Loop to access each cell. The given program segment explains the retrieval of the values from the array.
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  for (count =0; count < 6; count ++) { printf ("n %d value =", num [count]); } Memory Representation of Array Consider the following array declaration: int arr[8]; 16 bytes get immediately reserved in memory because each of the 8 integers would be 2 bytes long and since the array is not being initialized, all eight values present in it would be garbage values. Whatever be the initial values, all the array elements would always be present in contiguous memory location. This arrangement of array elements in memory is shown below. 12 34 66 -45 23 346 77 98 4002 4004 4006 4008 4010 4012 4014 4016 Value Address 1212 34 66 -45 23 346 77 98 4002 4004 4006 4008 4010 4012 4014 4016 Value Address In C, there is no check to see if the subscript used for an array exceeds the size of the array. Data entered with a subscript exceeding the array size will simply be placed in memory outside the array. This will lead to unpredictable results and there will be no error message to warn you that you are going beyond the array size. So to see to it that you do not reach beyond the array size is entirely the programmer's botheration and not the compiler's. Strings Just as a group of integers can be stored in an integer array, group of characters can be stored in a character array or "strings". The string constant is a one dimensional array of characters terminated by null character ('0'). This null character '0' (ASCII value 0) is different from 'O' (ASCII value 48). The terminating null character is important because it is the only way the function that works with string can know where the string ends. e.g.: Static char name [ ] = {'K', 'R', 'I', 'S', 'H', '0'}; This example shows the declaration and initialization of a character array. The array elements of a character array are stored in contiguous locations with each element occupying one byte of memory. K R I S H N A ‘0’ 4001 4002 4003 4004 4005 4006 4007 4009 NOTEOTE1. Contrary to the numeric array where a 5 digit number can be stored in one array cell, in the character arrays only a single character can be stored in one cell. So in order to store an array of strings, a 2-dimensional array is required. 2. As scanf( ) function is not capable of receiving multi word string, such strings should be Two Dimensional Array This is a table of four rows and three columns. Such a table of items can be defined using two dimensional arrays.
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  General form ofdeclaring a 2-D array is data_type array_name [row_size] [colum_size]; Initialization of a 2-Dimensional Array Two dimensional arrays may be initialized by a list of initial values enclosed in braces following their declaration. e.g.: static int table [2] [3] = {0, 0, 0, 1, 1, 1}; initializes the elements of the first row to 0 and the second row to one. The initialization is done by row. The aforesaid statement can be equivalently written as static int table [2] [3] = {{0, 0, 0}, {1, 1, 1}}; by surrounding the elements of each row by braces. We can also initialize a two dimensional array in the form of a matrix as shown below: static int table [2] [3] = {{0, 0, 0}, {1, 1, 1}}; The syntax of the above statement. Commas are required after each brace that closes off a row, except in the case of the last row. If the values are missing in an initializer, they are automatically set to 0. For instance, the statement static int table [2] [3] = {{1, 1}, {2}}; will initialize the first two elements of the first row to one, the first element of the second row to two, and all the other elements to 0. When all the elements are to be initialized to 0, the following short cut method may be used. static int m [3] [5] = {{0}, {0}, {0}}; The first element of each row is explicitly initialized to 0 while other elements are automatically initialized to 0. While initializing an array, it is necessary to mention the second (column) dimension, whereas the first dimension (row) is optional. Thus, the following declarations are acceptable. static int arr [2] [3] = {12, 34, 23, 45, 56, 45}; static int arr [ ] [3] = {12, 34, 23, 45, 56, 45 }; Memory Representation of Two Dimensional Array In memory, whether it is a one dimensional or a two dimensional array, the array elements are stored in one continuous chain. The arrangement of array elements of a two dimensional array of students, which contains roll numbers in one column and the marks in the other (in memory) is shown below:
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  1234 5002 5004 50065008 5010 5012 5014 5016 Value Address 1234 1234 1234 1234 1234 1234 1234 S[0][0] S[0][1] S[1][0] S[1][1] S[2][0] S[2][1] S[3][0] S[3][0]Notation 1234 5002 5004 5006 5008 5010 5012 5014 5016 Value Address 1234 1234 1234 1234 1234 1234 1234 S[0][0] S[0][1] S[1][0] S[1][1] S[2][0] S[2][1] S[3][0] S[3][0]Notation e.g.: 1. Program that stores roll number and marks obtained by a student side by side in a matrix main( ) { int stud [4] [2]; int i, j; for (i = 0; i < = 3; i++) { printf ("n Enter roll no. and marks"); scanf ("%d%d", &stud [i] [0], &stud[i] [1]); } for (i = 0; i < = 3; i++) printf ("%d%dn", stud [i] [0], stud [i] [0]; } There are two parts to the program, in the first part through a for Loop we read in the values of roll number and marks, whereas in second part through another for Loop we print out these values. Multi-dimensional Array C allows arrays of three or more dimensions. Multi-dimensional arrays are defined in much the same manner as one-dimensional arrays, except that a separate pair of square brackets is required for each subscript. The general form of a multi-dimensional array is data_type array_name [s1] [s2] [s3] . . . [sm]; e.g.: int survey [3] [5] [12]; float table [5] [4] [5] [3]; Here, survey is a 3-dimensional array declared to contain 180 integer_type elements. Similarly, table is a 4- dimensional array containing 300 elements of floating point type. An example of initializing a 4-dimensional array: static int arr [3] [4] [2] = {{{2, 4}, {7, 8}, {3, 4}, {5, 6},}, {{7, 6}, {3, 4}, {5, 3}, {2, 3}, }, {{8, 9}, {7, 2}, {3, 4}, {6, 1}, } }; In this example, the outer array has three elements, each of which is a two dimensional array of four rows, each of which is a one dimensional array of two elements.