class24-25 strings

8/7/2019 class24-25 Strings

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Dept of C.S.E., M.I.T., Manipal

Character Sequences

or strings


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Definition

A string is an array of characters. Any group of characters (except double quote sign)

defined between double quotation marks is a

constant string.

Character strings are often used to build meaningfuland readable programs.

The common operations performed on strings are

Reading and writing strings

Combining strings together Copying one string to another

Comparing strings to another

Extracting a portion of a string ..etc.


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Declaration and initialization.

char string_name[size];The size determines the number of characters in the

string_name.

For example, consider the following array:char jenny [20]; is an array that can store up to 20

elements of type char. It can be represented as:


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In the above array, we can store sequences of

characters up to 20 characters long.

But we can also store shorter sequences.

For example,An array jenny could store at some point in a program

either the sequence "Hello" or the sequence "Merry

Christmas", since both are shorter than 20 characters.


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The characters sequences "Hello"

and "Merry Christmas represented in an array jenny as

follows :


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Initialization of null-terminated

character sequences arrays of characters or strings are ordinaryarrays they follow the same rules of arrays.

For example, if we want to initialize an array of

characters with some predetermined sequence of

characters we can just do it like any other array:

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


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arrays of char elements have an additional method to

initialize their values: using string literals.

"the result is: " is a constant string literal.

For example,

char result[14] =the result is

Double quoted strings (") are literal constants whose

type is in fact a null-terminated array of characters. So

string literals enclosed between double quotes always

have a null character ('\0') automatically appended at the

end.


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we can initialize the array of char elements called

myword with a null-terminated sequence of

characters by either one of these two methods:char myword [ ] = { 'H', 'e', 'l', 'l', 'o', '\0' };

char myword [ ] = "Hello";

In both cases the array of characters myword is

declared with a size of 6 elements of type char: the 5

characters that compose the word "Hello" plus a final

null character ('\0') which specifies the end of the

sequence and that, in the second case, when using

double quotes (") null character ('\0') is appendedautomatically.

mystext = "Hello"; mystext[ ] = "Hello"; not validSTATEMENTS.


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Using null-terminated sequences of

characters#include void main ()

{

char question[] = "Please, enter your first name: ";char greeting[] = "Hello, ";

char yourname [80];

cout > yourname;

cout


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//include necessary header files.

void main()

{ const int MAX = 80; //max characters in string

char str[MAX]; //string variable str

cout > str; //put string in str

cout


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Reading Embedded Blanks

To read text containing blanks we use function,

cin :: get( ) // in C++

i.e cin.get(array_name, size)

The first argument to cin.get() is the array address

where the string being input will be placed.

The second argument specifies the maximum size of

the array, thus automatically avoiding buffer overrun.

or

in C Language we usegets(string) to read everything that you enter from

the key board until the ENTER key is pressed.


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//include necessary header files.

void main(){ const int MAX = 80; //max characters in string

char str[MAX]; //string variable str

cout


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#include#include//#include //for gets and puts

//Count the number of characters in a stringvoid main(){const int Max = 100;char sent[Max];

int i=0,count=0;clrscr();cout


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#include#include

//#include//Count the number of words in a sentencevoid main(){const int MAX = 100;char sent[MAX];

int i=0,count=1;clrscr();cout


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Reading Multiple Lines

we use third argument in cin::get() function.

cin.get(array_name, size, stop_char)

The argument stop_char specifies the character that tells

the function to stop reading. The default value for this

argument is the newline (\n) character, but if you call the

function with some other character for this argument, the

default will be overridden by the specified character.


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//include necessary header files

void main()

{

const int MAX = 200; //max characters in stringchar str[MAX]; //string variable str

cout


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String length can be obtained by using thefollowing functionn=strlen(string)This function counts and returns the numberof characters in a string.where n is an integer variable which receives

the value of the length of thestring. The argument may be a stringconstant.

Copying a String the Hard WayThe best way to understand the true nature of

strings is to deal with them character bycharacter. The following program does this.


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// copies a string using a for loop

#include

#include

void main()

{

char str1[ ] = Oh, Captain, my Captain! our fearful tripis done;

const int MAX = 80; //size of str2 bufferchar str2[MAX]; //empty string

for(int j=0 ; j


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The copying is done one character at a time, in the

Statement str2[j] = str1[j];

The copied version of the string must be terminated with anull. However, the string length returned by strlen() does

not include the null. We could copy one additional

character, but its safer to insert the null explicitly. We do

this with the line str2[j] = \0;If you dont insert this character, youll find that the string

printed by the program includes all sorts of weird

characters following the string you want. The


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Copying a String the Easy Way

strcpy(destination, source)

The strcpy function works almost like a stringassignment operator and assigns the contents of sourceto destination.

source may be a character array variable or a stringconstant.

e.g., strcpy(city,DELHI); will assign the string DELHI to the string variable city.

Similarly, the statement strcpy(city1,city2);

will assign the contents of the string variable city2 to the

string variable city1.The size of the array city1 should be large enough toreceive the contents of city2.


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//include necessary header filesvoid main()

{

char str1[ ] = Tiger, tiger, burning bright\n;

const int MAX = 80; //size of str2 buffer

char str2[MAX]; //empty stringstrcpy(str2, str1); //copy str1 to str2

cout


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Arrays of Strings

Heres an example, that puts the names of the days of the

week in an array:

// array of strings

void main()

{ const int DAYS = 7; //number of strings in array

const int MAX = 10; //maximum size of each string

//array of strings

char star[DAYS][MAX] = { Sunday, Monday, Tuesday,Wednesday, Thursday, Friday, Saturday };

for(int j=0; j


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strcmp( ) Function :

The strcmp function compares two strings identified bythe arguments and has a value 0 if they are equal.

If they are not, it has the numeric difference betweenthe first non matching characters in the strings.It takes the form strcmp(string1,string2);string1 and string2 may be string variables or stringconstants.

Our major concern is to determine whether the stringsare equal; if not, which is alphabetically above. Thevalue of the mismatch is rarely important.e.g., strcmp(their,there); will return a value of 9which is the numeric difference between ASCII i andASCII r. That is, i minus r in ASCII code is 9.If the value is negative, string1 is alphabetically abovestring2.


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strcat( ) Function :

The strcat function joins two strings together.

It takes the following form:

strcat(string1,string2);string1 and string2 are character arrays.

When the function strcat is executed, string2 isappended to a string1. It does so by removing thenull character at the end of string1 and placingstring2 from there. The string at string2 remains

unchanged.


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#include#include

#include#includevoid main(){

char s1[40], s2[50];cout


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Two Dimensional Character Arrays

These Are arrays of arrays. 2-D character array consistsof strings as its individual elements.

Declaration :-

char a[10][10];

Initialization:-

char a[10][20]={aaa ,

bbb,

ccc

};


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void main(){

char string[30][30];int no,i;coutno;cout


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void main(){char string[30][30],temp[30];int no,i,j;coutno;cout


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for(i=0;i


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void main()

{char str[30];int i,n,j,flag=1;cout


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void main(){

char str[70];char temp;int i,n=0;cout


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void main(){

char c;

clrscr();

cout


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void main(){char string[30];int i,n=0;cout


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#include

#include

#include

//Checking for given substring in a string

char name[10], sub[10],flag=0,pos;

int i, j,k,l;

coutname;

l=strlen(name);coutsub;

int m=strlen(sub);

j=0,i=0;

while(sub[j]!='\0')

{ flag=0;


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if(sub[j]!=name[i])

{i++; continue;}

else pos=i;

if ((i+m)

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