Unit 8

Character Arrays and Strings

1. Explain character array with example

Strings are actually one-dimensional array of characters terminated by a null character '\0'. Thus a null-terminated string contains the characters that comprise the string followed by a null.

The following declaration and initialization create a string consisting of the word "Hello". To hold the null character at the end of the array, the size of the character array containing the string is one more than the number of characters in the word "Hello."

Char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

If you follow the rule of array initialization then you can write the above statement as follows −

Char greeting[] = "Hello";

Following is the memory presentation of the above defined string in C/C++ −

Actually, you do not place the null character at the end of a string constant. The C compiler automatically places the '\0' at the end of the string when it initializes the array. Let us try to print the above mentioned string −

#include <stdio.h>

Int main () {

   char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

   printf("Greeting message: %s\n", greeting );

   return 0;

}

When the above code is compiled and executed, it produces the following result −

Greeting message: Hello

2.     Explain functions that manipulate null-terminated strings  with examples

The following example uses some of the above-mentioned functions −

#include <stdio.h>

#include <string.h>

Int main () {

   char str1[12] = "Hello";

   char str2[12] = "World";

   char str3[12];

   int  len ;

   /* copy str1 into str3 */

   strcpy(str3, str1);

   printf("strcpy( str3, str1) :  %s\n", str3 );

   /* concatenates str1 and str2 */

   strcat( str1, str2);

   printf("strcat( str1, str2):   %s\n", str1 );

   /* total lenghth of str1 after concatenation */

   len = strlen(str1);

   printf("strlen(str1) :  %d\n", len );

   return 0;

}

When the above code is compiled and executed, it produces the following result −

Strcpy( str3, str1) :  Hello

Strcat( str1, str2):   HelloWorld

Strlen(str1) :  10

3.     Explain Numeric Array in detail with example

Arrays a kind of data structure that can store a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

Instead of declaring individual variables, such as number0, number1, ..., and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and ..., numbers[99] to represent individual variables. A specific element in an array is accessed by an index.

All arrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.

Declaring Arrays

To declare an array in C, a programmer specifies the type of the elements and the number of elements required by an array as follows −

Type arrayName [ arraySize ];

This is called a single-dimensional array. The arraySize must be an integer constant greater than zero and type can be any valid C data type. For example, to declare a 10-element array called balance of type double, use this statement −

Double balance[10];

Here balance is a variable array which is sufficient to hold up to 10 double numbers.

Initializing Arrays

You can initialize an array in C either one by one or using a single statement as follows −

Double balance[5] = {1000.0, 2.0, 3.4, 7.0, 50.0};

The number of values between braces { } cannot be larger than the number of elements that we declare for the array between square brackets [ ].

If you omit the size of the array, an array just big enough to hold the initialization is created. Therefore, if you write −

Double balance[] = {1000.0, 2.0, 3.4, 7.0, 50.0};

You will create exactly the same array as you did in the previous example. Following is an example to assign a single element of the array −

Balance[4] = 50.0;

The above statement assigns the 5th element in the array with a value of 50.0. All arrays have 0 as the index of their first element which is also called the base index and the last index of an array will be total size of the array minus 1. Shown below is the pictorial representation of the array we discussed above −

Accessing Array Elements

An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array. For example −

Double salary = balance[9];

The above statement will take the 10th element from the array and assign the value to salary variable. The following example Shows how to use all the three above mentioned concepts viz. Declaration, assignment, and accessing arrays −

#include <stdio.h>

Int main () {

   int n[ 10 ]; /* n is an array of 10 integers */

   int i,j;

   /* initialize elements of array n to 0 */        

   for ( i = 0; i < 10; i++ ) {

      n[ i ] = i + 100; /* set element at location i to i + 100 */

   }

   /* output each array element's value */

   for (j = 0; j < 10; j++ ) {

      printf("Element[%d] = %d\n", j, n[j] );

   }

   return 0;

}

When the above code is compiled and executed, it produces the following result −

Element[0] = 100

Element[1] = 101

Element[2] = 102

Element[3] = 103

Element[4] = 104

Element[5] = 105

Element[6] = 106

Element[7] = 107

Element[8] = 108

Element[9] = 109

Arrays in Detail

Arrays are important to C and should need a lot more attention. The following important concepts related to array should be clear to a C programmer −

4.     What is Null Character?

A null character is a character with all its bits set to zero. Therefore, it has a numeric value of zero and can be used to represent the end of a string of characters, such as a word or phrase. This helps programmers determine the length of strings. In practical applications, such as database and spreadsheet programs, null characters are used as fillers for spaces.

5.     Explain string with example

String is nothing but a collection of characters in a linear sequence. 'C' always treats a string a single data even though it contains whitespaces. A single character is defined using single quote representation. A string is represented using double quote marks.

Example, "Welcome to the world of programming!"

'C' provides standard library <string.h> that contains many functions which can be used to perform complicated string operations easily.

Declare and initialize a String

A string is a simple array with char as a data type. 'C' language does not directly support string as a data type. Hence, to display a string in 'C', you need to make use of a character array.

The general syntax for declaring a variable as a string is as follows,

Char string_variable_name [array_size];

The classic string declaration can be done as follow:

Char string_name[string_length] = "string";

The size of an array must be defined while declaring a string variable because it used to calculate how many characters are going to be stored inside the string variable. Some valid examples of string declaration are as follows,

Char first_name[15];    //declaration of a string variable

Char last_name[15];

The above example represents string variables with an array size of 15. This means that the given character array is capable of holding 15 characters at most. The indexing of array begins from 0 hence it will store characters from a 0-14 position. The C compiler automatically adds a NULL character '\0' to the character array created.

6.     Write program to read the 2D array of characters or array of String in C

#include<stdio.h>

Int main()

{

  // declaring and initializing 2D String

  char language[5][10] =

     {"Java", "Python", "C++", "HTML", "SQL"};

  // Dispaying strings

  printf("Languages are:\n");

  for(int i=0;i<5;i++)

  puts(language[i]);

  return 0;

}

Output:-

Languages are:
Java
Python
C++
HTML
SQL

Program:- Write a program to read and display a 2D array of strings in C language.

#include<stdio.h>

Int main()

{

     char name[10][20];

     int i,n;

     printf("Enter the number of names (<10): ");

     scanf("%d",&n);

     // reading string from user

     printf("Enter %d names:\n",n);

     for(i=0; i<n; i++)

     scanf("%s[^\n]",name[i]);

     // Dispaying strings

     printf("\nEntered names are:\n");

     for(i=0;i<n;i++)

     puts(name[i]);

     return 0;

}

Output:-

Enter the number of names (<10): 5
Enter 5 names:
Emma
Olivia
Ava
Isabella
Sophia

Entered names are:
Emma
Olivia
Ava
Isabella
Sophia

7.     Write a program for Reading and displaying 2d array of strings in C

The two-dimensional array of strings can be read by using loops. To read we can use scanf(), gets(), fgets() or any other methods to read the string.

// reading strings using for loop    

For(i=0;i<n;i++)

{

  scanf("%s[^\n]",name[i]);

}

Or,

// reading strings using while loop

Int i=0;

While(i<n)

{

  scanf("%s[^\n]",name[i]);

  i++;

}

The two-dimensional array of strings can be displayed by using loops. To display we can use printf(), puts(), fputs() or any other methods to display the string.

// displaying strings using for loop

For(i=0;i<n;i++)

{

  puts(name[i]);

}

Or,

// displaying strings using while loop

Int i=0;

While (i<n)

{

  puts(name[i]);

  i++;

}

8.     Explain Initialization of array of strings

Two dimensional (2D) strings in C language can be directly initialized as shown below,

Char language[5][10] = {"Java", "Python", "C++", "HTML", "SQL"};

Char largestcity[6][15] =

    {"Tokyo", "Delhi", "Shanghai", "Mumbai", "Beijing", "Dhaka"};

The two dimensional (2D) array of Strings in C also can be initialized as,

Char language[5][10] ={

                         {'J','a','v','a','\0'},

                         {'P','y','t','h','o','n','\0'},

                         {'C','+','+','\0'},

                         {'H','T','M','L','\0'},

                         {'S','Q','L','\0'}

                      };

Since it is a two-dimension of characters, so each String (1-D array of characters) must end with null character i.e. ‘\0’

The second way of declaring the array of strings is a lengthy process, and other programmers can’t read them easily compared to the previous declaration, that why most of the time we prefer the first declaration.

The each String in this array can be accessed by using its index number. The index of array always starts with 0.

Language[0] => "Java";

Language[1] => "Python";

Language[2] => "C++";

Language[3] => "HTML";

Language[4] => "SQL";

Note1:- the number of characters (column-size) must be declared at the time of the initialization of the two-dimensional array of strings.

// it is valid

Char language[ ][10] = {"Java", "Python", "C++", "HTML", "SQL"};

But that the following declarations are invalid.

// invalid

Char language[ ][ ] = {"Java", "Python", "C++", "HTML", "SQL"};

// invalid

Char language[5][ ] = {"Java", "Python", "C++", "HTML", "SQL"};

Note2:- Once we initialize the array of String then we can’t directly assign a new String.

Char language[5][10] = {"Java", "Python", "C++", "HTML", "SQL"};

// now, we can't directly assign a new String

Language[0] = "Kotlin"; // invalid

// we must copy the String

Strcpy(language[0], "Kotlin"); // valid

// Or,

Scanf(language[0], "Kotlin"); // valid

9.     Explain 2 dimensional array in detail

Sometimes we often use lists of character strings, such as the list of names of students in a class, a list of names of employees in an organization, a list of places, etc. A list of names can be treated as a table of string. To store the entire list we use a 2d array of strings in C language.

The array of characters is called a string. “Hi”, “Hello”, and e.t.c are the examples of String. Similarly, the array of Strings is nothing but a two-dimensional (2D) array of characters. To declare an array of Strings in C, we must use the char data type.

Example of two dimensional characters or the array of Strings is,

Char language[5][10] = {"Java", "Python", "C++", "HTML", "SQL"};

Declaration of the array of strings

Syntax:-

Char string-array-name[row-size][column-size];

Here the first index (row-size) specifies the maximum number of strings in the array, and the second index (column-size) specifies the maximum length of every individual string.

For example, char language[5][10]; In the “language” array we can store a maximum of 5 Strings and each String can have a maximum of 10 characters.

In C language, each character take 1 byte of memory. For the “language” array it will allocate 50 bytes (1*5*10) of memory. Where each String will have 10 bytes (1*10) of memory space.

10. What are some of the Library Functions in header string?

Following are the functions defined in the header string.h −