Unit 8

Character Arrays and Strings

8.1 Difference of character array with numeric array and importance of NULL character.

Character array

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

C supports a wide range of functions that manipulate null-terminated strings −

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

Numeric Array

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 −

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.

8.2 Declaration, Initialization and various input and output methods of string, formatted output of string, arithmetic operations on characters.

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.

Let's study the initialization of a string variable. Following example demonstrates the initialization of a string variable,

Char first_name[15] = "ANTHONY";

Char first_name[15] = {'A','N','T','H','O','N','Y','\0'}; // NULL character '\0' is required at end in this declaration

Char string1 [6] = "hello";/* string size = 'h'+'e'+'l'+'l'+'o'+"NULL" = 6 */

Char string2 [ ] = "world";  /* string size = 'w'+'o'+'r'+'l'+'d'+"NULL" = 6 */

Char string3[6] = {'h', 'e', 'l', 'l', 'o', '\0'} ; /*Declaration as set of characters ,Size 6*/

In string3, the NULL character must be added explicitly, and the characters are enclosed in single quotation marks.

'C' also allows us to initialize a string variable without defining the size of the character array. It can be done in the following way,

Char first_name[ ] = "NATHAN";

The name of a string acts as a pointer because it is basically an array.

String Input: Read a String

When writing interactive programs which ask the user for input, C provides the scanf(), gets(), and fgets() functions to find a line of text entered from the user.

When we use scanf() to read, we use the "%s" format specifier without using the "&" to access the variable address because an array name acts as a pointer. For example:

#include <stdio.h>

Int main() {

Char name[10];

Int age;

Printf("Enter your first name and age: \n");

Scanf("%s %d", name, &age);

Printf("You entered: %s %d",name,age);

}

Output:

Enter your first name and age:

John_Smith 48

The problem with the scanf function is that it never reads an entire string. It will halt the reading process as soon as whitespace, form feed, vertical tab, newline or a carriage return occurs. Suppose we give input as "Guru99 Tutorials" then the scanf function will never read an entire string as a whitespace character occurs between the two names. The scanf function will only read Guru99.

In order to read a string contains spaces, we use the gets() function. Gets ignores the whitespaces. It stops reading when a newline is reached (the Enter key is pressed).For example:

#include <stdio.h>

Int main() {

Char full_name[25];

Printf("Enter your full name: ");

Gets(full_name);

Printf("My full name is %s ",full_name);

Return 0;

}

Output:

Enter your full name: Dennis Ritchie

My full name is Dennis Ritchie

Another safer alternative to gets() is fgets() function which reads a specified number of characters. For example:

#include <stdio.h>

Int main() {

Char name[10];

Printf("Enter your  name plz: ");

Fgets(name, 10, stdin);

Printf("My name is %s ",name);

Return 0;}

Output:

Enter your name plz: Carlos

My name is Carlos

The fgets() arguments are :

• The string name,
• The number of characters to read,
• Stdin means to read from the standard input which is the keyboard.

String Output: Print/Display a String

The standard printf function is used for printing or displaying a string on an output device. The format specifier used is %s

Example,

Printf("%s", name);

String output is done with the fputs() and printf() functions.

Fputs() function

The fputs() needs the name of the string and a pointer to where you want to display the text. We use stdout which refers to the standard output in order to print to the screen.For example:

#include <stdio.h>

Int main()

{char town[40];

Printf("Enter your town: ");

Gets(town);

Fputs(town, stdout);

Return 0;}

Output:

Enter your town: New York

New York

Puts function

The puts function prints the string on an output device and moves the cursor back to the first position. A puts function can be used in the following way,

#include <stdio.h>

Int main() {

Char name[15];

Gets(name);        //reads a string

Puts(name);        //displays a string

Return 0;}

The syntax of this function is comparatively simple than other functions.

The string library

The standard 'C' library provides various functions to manipulate the strings within a program. These functions are also called as string handlers. All these handlers are present inside <string.h> header file.

Lets consider the program below which demonstrates string library functions:

#include <stdio.h>

#include <string.h>

Int main () {

//string initialization

Char string1[15]="Hello";

Char string2[15]=" World!";

Char string3[15];

Int val;

//string comparison

Val= strcmp(string1,string2);

If(val==0){

Printf("Strings are equal\n");

}

Else{

Printf("Strings are not equal\n");

}

//string concatenation

Printf("Concatenated string:%s",strcat(string1,string2)); //string1 contains hello world!

//string length

Printf("\nLength of first string:%d",strlen(string1));

Printf("\nLength of second string:%d",strlen(string2));

//string copy

Printf("\nCopied string is:%s\n",strcpy(string3,string1));  //string1 is copied into string3

Return 0;

}

Output:

Strings are not equal

Concatenated string:Hello World!

Length of first string:12

Length of second string:7

Copied string is:Hello World!

Other important library functions are:

• Strncmp(str1, str2, n) :it returns 0 if the first n characters of str1 is equal to the first n characters of str2, less than 0 if str1 < str2, and greater than 0 if str1 > str2.
• Strncpy(str1, str2, n) This function is used to copy a string from another string. Copies the first n characters of str2 to str1
• Strchr(str1, c): it returns a pointer to the first occurrence of char c in str1, or NULL if character not found.
• Strrchr(str1, c): it searches str1 in reverse and returns a pointer to the position of char c in str1, or NULL if character not found.
• Strstr(str1, str2): it returns a pointer to the first occurrence of str2 in str1, or NULL if str2 not found.
• Strncat(str1, str2, n) Appends (concatenates) first n characters of str2 to the end of str1 and returns a pointer to str1.
• Strlwr() :to convert string to lower case
• Strupr() :to convert string to upper case
• Strrev() : to reverse string

Converting a String to a Number

In C programming, we can convert a string of numeric characters to a numeric value to prevent a run-time error. The stdio.h library contains the following functions for converting a string to a number:

• Int atoi(str) Stands for ASCII to integer; it converts str to the equivalent int value. 0 is returned if the first character is not a number or no numbers are encountered.
• Double atof(str) Stands for ASCII to float, it converts str to the equivalent double value. 0.0 is returned if the first character is not a number or no numbers are encountered.
• Long int atol(str) Stands for ASCII to long int, Converts str to the equivalent long integer value. 0 is returned if the first character is not a number or no numbers are encountered.

The following program demonstrates atoi() function:

#include <stdio.h>

Int main()

{char *string_id[10];

Int ID;

Printf("Enter a number: ");

Gets(string_id);

ID = atoi(string_id);

Printf("you enter %d  ",ID);

Return 0;}

Output:

Enter a number: 221348

You enter 221348

• A string pointer declaration such as char *string = "language" is a constant and cannot be modified.

Summary

• A string is a sequence of characters stored in a character array.
• A string is a text enclosed in double quotation marks.
• A character such as 'd' is not a string and it is indicated by single quotation marks.
• 'C' provides standard library functions to manipulate strings in a program. String manipulators are stored in <string.h> header file.
• A string must be declared or initialized before using into a program.
• There are different input and output string functions, each one among them has its features.
• Don't forget to include the string library to work with its functions
• We can convert string to number through the atoi(), atof() and atol() which are very useful for coding and decoding processes.
• We can manipulate different strings by defining a string array.

Formatted output of string

The format specifier is used during input and output. It is a way to tell the compiler what type of data is in a variable during taking input using scanf() or printing using printf(). Some examples are %c, %d, %f, etc.

The format specifier in printf() and scanf() are mostly the same but there is some difference which we will see.

Printf(char *format, arg1, arg2, …)

This function prints the character on standard output and returns the number of character printed the format is a string starting with % and ends with conversion character (like c, i, f, d, etc.).
Between both, there can be elements governing the printing format. Below is its description

1. A minus(-) sign tells left alignment.
2. A number after % specifies the minimum field width to be printed if the characters are less than the size of width the remaining space is filled with space and if it is greater than it printed as it is without truncation.
3. A period( . ) symbol separate field width with the precision.

Precision tells the maximum number of digits in integer, characters in string and number of digits after decimal part in floating value.

Lets see these..
Character format specifier : %c

Output:

A

Integer format specifier : %d, %i

Output:

45

45

Floating-point format specifier : %f, %e or %E

Output:

12.670000

1.267000e+01

Unsigned Octal number for integer : %o

Output:

103

Unsigned Hexadecimal for integer : %x, %X

Output:

f

String printing : %s

Output:

Geeksforgeeks

More formatting

Output:

Geeksforgeeks

Geeksforgeeks      

Geeks

Geeks

Scanf(char *format, arg1, arg2, …)

This function take input using standard input (keyboard) and store it in variable accordingly. It returns the number of items successfully read. Formal parameter arg1, agr2, .. Must be a pointer

Decimal integer : %d

Integer may be octal or in hexadecimal : %i

Double floating-point number : %lf

Output:

45.650000

String input : %s  

Output:

P@

Character input : %c  

Many other format specifiers are also there
1.%u for an unsigned integer.
2.%lld for long long int.
3.%o octal integer without leading zero
4.%x hexadecimal integer without 0x before the number.

Arithmetic operations on characters

Character arithmetic is used to implement arithmetic operations like addition and subtraction on characters in C language. It is used to manipulate the strings. When the characters are used with the arithmetic operations, it converts them into integer value automatically i.e. ASCII value of characters.

Here is an example of character arithmetic in C language,

Example

#include <stdio.h>

Int main(){

Char s = 'm';

Char t = 'z' - 'y';

Printf("%d\n", s);

Printf("%c\n", s);

Printf("%d\n", (s+1));

Printf("%c\n", (s+1));

Printf("%d\n", (s-1));

Printf("%c\n", (s-1));

Printf("%d\n", t);

// printf("%c", t);

Return 0;

}

Output

Here is the output −

109

m

110

n

108

l

1

8.3 Various functions of string.h: strlen, strcat, strcmp, strcpy, strrev, strstr, etc.

The string.h header defines one variable type, one macro, and various functions for manipulating arrays of characters.

Library Variables

Following is the variable type defined in the header string.h −

Library Macros

Following is the macro defined in the header string.h −

Library Functions

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

8.4 Two dimensional character array (table of strings).

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.

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

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++;

}

Sample 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