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Wednesday, September 7, 2011

How are strings and arrays defined in C?

A string can be defined as a group of characters, usually letters of the alphabet. When C is either to compare a string with another string, output it, copy it to another string, or whatever, the functions are intended to do what they are called to do until a null, which is a zero, is detected. Such strings are often called an ASCII-Z string. C treats a string as an array termination with a NULL character. C does not have a separate data type for strings and so strings exist as the arrays of characters. An extra byte must be left to store the NULL “\0”. Strings are declared as the arrays of characters. For example:

char name[25];

Strings can be fully or partially initialized depending on the requirements of the user. For example:
char fill[10] = { ‘a’, ‘ ‘, ‘r’,’o’,’p’,’l’,’a’,’n’,’e’,’\0’ };

There exist certain predefined functions for modifying strings. The library cstring.h houses all these functions. Strcpy() is used to copy one string into another string. Strlen() is used to determine the length of the string. Strcmp() is function for comparing two strings i.e., which one is bigger in terms of length. Strcat() is used to concatenate two strings. The second string is appended to the end of the first string. Strrev() is used to reverse a string alphabetically.

An array is a C derived data type and can be defined as a collection of variables of the same data type that are referenced by a common name. All arrays consist of contiguous memory locations where the lowest address corresponds to the first element and highest address corresponds to the last element. Arrays are useful when quite many elements of the same data type are needed to be stored and processed. The numbers in [ ] are called indices or subscripts. A string itself is an array of characters. Arrays are of two types namely one- dimensional arrays and multi dimensional arrays. Multi dimensional array comprises of elements which themselves are arrays. The general form of an array declaration is as follows:

Type array-name [size];

Here type states the data type of the array elements. The array name declares the name of the array, and finally the size defines how many elements will be there in the array. The data type of the array is called the base type.

A multidimensional array consists of M*N elements where M is the number of rows and N is the number of columns. It can be declared as follows:

Type array-name [rows][columns];

Where single dimensional arras can be read using a single loop, it takes nested loops to read and access the elements of a multi dimensional array. One loop is used to process the rows and the other one is used to process the columns. The arrays can be initialized during the run time as follows:

Type array-name [size 1]……….[size N]= {value list};

The value list consists of the array elements. C allows you to skip the size of arrays in an initialization statement. These types of arrays are called unsized arrays. For example:
Int abc[ ] = {1,2,3,5,7};

The best way to assign values to an array is using a "for" or "while" loop because it’s not affordable to write a separate initialization for every element. Arrays can be passed s parameters to the functions to maintain a structured design. Always keep in mind that in C subscripts start from 0. A string from an array of strings can be accessed by using pointers. But keep in mind that pointers hold only address of the strings. From there it is able to obtain the whole chunk of the contiguous memory.

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