STRINGS IN C PRESENTED BY: ER. SUMANPREET KAUR LECTURER IN CE DEPTT. GPCG ASR.

STRINGS INC

PRESENTED BY:

ER. SUMANPREET KAUR

LECTURER IN CE DEPTT.

GPCG ASR.

Topics Covered Are:

1. Introduction2. Declaration of strings3. Initialization of strings4. Reading strings5. Writing strings6. String handling functions7. Array of strings8. Conclusion

1. Intoduction

• String is sequence or collection of characters terminated by null character.

• Null terminates the string but not part of it.

• Strings are accessed through arrays/ pointer .

• String.h contains prototypes of many useful functions.

1.1 Features of strings

1. C has no native string type, instead we use arrays of char.

2. A special character, called a “null”, marks the end.

3. This may be written as ’\0’.4. This is the only character whose ASCII

value is zero.5. Depending on how arrays of characters

are built, we may need to add the null by hand , or the compiler may add it for us.

2. Declaration of strings

The strings can be declared as array of character.The general syntax is:

char name_of_string[length];

Char is data type.

Name_of _string is user defined name given to string variable.

[length]: defines the size of the string.

Example of declaration of strings

char a[10]; in above example ‘a’ is string variable of length 10 characters. char a[]={‘H’, ’A’, ’N’, ’D’ ,’A’, ’\0’,};In memory the character array or string is cont.…

a[0] a[1] a[2] a[3] a[4] a[5]

H A N D A \0

Mem 200 201 202 203 204 205 Add.

So total 6 bytes are allocated to the string ‘a’.

cont. …

CONTD. …

Notice that even though there are only five characters in the world ‘HONDA’ , six characters are stored in computer. The last character, the character’/0’ is the NULL character, which indicates the end of string.

Therefore , if any array of characters is to be used to store a string , the array must be large enough to store the string and its terminating NULL character.

3.Initialization of strings we can itialize string variables at

compile time such as: char name[10]=“Arris”; This initialization creates the following

spaces in storage: [0] [1] [2] [3] [4] [5] [6] [7] [8] [9]

A r r i s \0 \0 \0 \0 \0

Contd. …….

Initialization of strings if we happen to declare a string like this : char my_drink[3]= “tea”; we will get the following syntax error: error c2117:’tea’: array bound overflow . instead , we need to at lest declare the array with (the size of string +1) to accommodate the null terminate character’\0’. char my_drink[4]=“tea”;

String InputUse %s field specification in scanf to read string

◦ ignores leading white space◦ reads characters until next white space

encountered◦ C stores null (\0) char after last non-white space

char◦ Reads into array (no & before name, array is a

pointer)Example:

char Name[11];scanf(“%s”,Name);

Problem: no limit on number of characters read (need one for delimiter), if too many characters for array, problems may occur

String Input (cont)Can use the width value in the field

specification to limit the number of characters read:char Name[11];scanf(“%10s”,Name);

Remember, you need one space for the \0◦width should be one less than size of

arrayStrings shorter than the field specification

are read normally, but C always stops after reading 10 characters

String Input (cont)Edit set input %[ListofChars]

◦ ListofChars specifies set of characters (called scan set)

◦ Characters read as long as character falls in scan set◦ Stops when first non scan set character encountered◦ Note, does not ignored leading white space◦ Any character may be specified except ]◦ Putting ^ at the start to negate the set (any character

BUT list is allowed)Examples:

scanf(“%[-+0123456789]”,Number);scanf(“%[^\n]”,Line); /* read until newline char */

String OutputUse %s field specification in printf:

characters in string printed until \0 encountered

char Name[10] = “Rich”;

printf(“|%s|”,Name); /* outputs |Rich| */Can use width value to print string in space:

printf(“|%10s|”,Name); /* outputs | Rich| */

Use - flag to left justify:

printf(“|%-10s|”,Name); /* outputs |Rich | */

Input/Output Example#include <stdio.h>

void main() { char LastName[11]; char FirstName[11];

printf("Enter your name (last , first): "); scanf("%10s%*[^,],%10s",LastName,FirstName);

printf("Nice to meet you %s %s\n", FirstName,LastName);}

Example cont…

Enter your name(last , first):Kaur Harpreet

Nice to meet you Harpreet Kaur

Readind a string The drawback of reading a string

using scanf() is that it does not read whitespaces or whole line

If the string to be read as an input has embedded whitespace characters, use standard gets() function.

Printing a stringThe drawback of printing a string

using printf() is that it does not print whitespaces.

If the string to be print as an output has embedded whitespace characters, use standard puts() function.

Example of gets()/puts()

#include <stdio.h>

void main(void){

char string1[50]; char string2[50];

printf("Enter a string less than 50 characters with spaces: \n "); gets(string1);

printf("\nYou have entered: "); puts(string1);

getch();

}

Example cont…

/* Sample output */Enter a string less than 50 characters with spaces: hello world

You have entered: hello world

String handling functionsC provides a wide range of string functions

for performing different string tasksExamples

strlen(str) - calculate string lengthstrcpy(dst,src) - copy string at src to dststrcmp(str1,str2) - compare str1 to str2

Functions come from the utility library string.h◦#include <string.h> to use

Commonly used functions

Function Description

Strlen() To calculate the length of string.

Strcpy() To copy the contents of one string to another

Strcat() To concatenate the two strings

Strcmp() To compare two strings

Strstr() To find the first occurrence of a substring in another string

Strrev() Reverse string

Strlwr() Converts a string to lowercase

Strupr() Converts the string to uppercase

Strset() Sets all characters of string to a given number

String Length strln() strln() counts the number of characters in a

string. Syntax: int strlen(char *str)

returns the length (integer) of the string argument

counts the number of characters until an \0 encountered

does not count \0 char

Example:char str1 = “hello”;strlen(str1) would return 5

String copy strcpy() Strcpy() copies the contents of one string into

another string. Syntax: char *strcpy(char *dst, char *src)

ocopies the characters (including the \0) from the source string (src) to the destination string (dst)

odst should have enough space to receive entire string (if not, other data may get written over)

o if the two strings overlap (e.g., copying a string onto itself) the results are unpredictable

o return value is the destination string (dst)

String copy strcpy() cont. ..Example:

#include<stdio.h>

#include<conio.h>

Void main()

{

char source[]=“rajaesh”;

char target[20];

strcpy(target,source);

printf(“source string=%s\n”,source);

printf(“target string=%s\n”,target);

getch();

}

String copy strcpy() cont. ..

Output of above example: source string= rajesh target string = rajesh

Example: strcpy#include <stdio.h>

#include <string.h>

void main(void)

{

char string1[100] = "Malaysia";

char string2[50] = "Gemilang";

strncpy(string1, string2, 4);

printf(“string1: %s\n", string1);

}

Output:

string1: Gemiysia

String comparison strcmp()

Syntax:

int strcmp(char *str1, char *str2)compares str1 to str2, returns a value based on

the first character they differ at:less than 0

if ASCII value of the character they differ at is smaller for str1

or if str1 starts the same as str2 (and str2 is longer)

String comparison strcmp()greater than 0

if ASCII value of the character they differ at is larger for str1

or if str2 starts the same as str1 (and str1 is longer)

0 if the two strings do not differ

String Comparison (cont)

strcmp examples:strcmp(“hello”,”hello”) -- returns 0

strcmp(“yello”,”hello”) -- returns value > 0

strcmp(“Hello”,”hello”) -- returns value < 0

strcmp(“hello”,”hello there”) -- returns value < 0

strcmp(“some diff”,”some dift”) -- returns value < 0

expression for determining if two strings s1,s2 hold the same string value:!strcmp(s1,s2)

String Comparison (cont)Sometimes we only want to compare first n chars:

int strncmp(char *s1, char *s2, int n)

Works the same as strcmp except that it stops at the nth character

looks at less than n characters if either string is shorter than n

strcmp(“some diff”,”some DIFF”) -- returns value > 0

strncmp(“some diff”,”some DIFF”,4) -- returns 0

String Comparison (ignoring case)

Syntax:int strcasecmp(char *str1, char *str2)

similar to strcmp except that upper and lower case characters (e.g., ‘a’ and ‘A’) are considered to be equal

int strncasecmp(char *str1, char *str2, int n)

version of strncmp that ignores case

String Concatenation strcat()Concatenates the source string at the end of the target string.

Syntax: strcat(string1, string 2);

Example: strcat/* Concatenating Strings Using strcat */#include <stdio.h> #include <string.h> void main() {

char str1[50] = "Hello "; char str2[ ] = "World"; strcat(str1, str2); printf("str1: %s\n", str1);

}

Example: strcat cont. …Output:

str1: Hello World

Note : This only works if you've defined the str1 array to be large enough to hold the characters of your string. If you don't specify a size, the program may crash.

Example: strncat/* Concatenating Strings Using strncat */#include <stdio.h> #include <string.h> void main() {

char str1[50] = "Hello "; char str2[ ] = "World"; strncat(str1, str2, 2); printf("str1: %s\n", str1);

}Output:

str1: Hello Wo

Program to reverses all characters in a stringmain(){char *str=“string”;printf(“before reversing string: %s\n”, str);strrev(str);printf(“after reversing string: %s\n”, str);

}OUTPUTbefore reversing string: stringafter reversing string: gnirts

Program to find the first occurrence of a substring in another string main(){

char*str1=“International airport:”,*str2=“nation”,*ptr;ptr= strstr(str1,str2);printf(“the substring is: %\n”,ptr);

}OUTPUTthe substring is: national airport

Program to convert a string to all lowercasemain(){char *str=“International Airport”;printf(“string prior to strlwr: %s\n”, str);

strlwr(str);printf(“string after strlwr: %s\n”, str);

}OUTPUT:string prior to strlwr:International Airportstring after strlwr: international airport

Array of strings

Arrays of strings can be declared and handled in a similar manner to that described for 2-D

Dimensional arrays.

Syntax:

<data type><name of string>[number of strings] [number of characters];

Array of stringsSometimes useful to have an array of

string valuesEach string could be of different length

(producing a ragged string array)Example:

char *MonthNames[13]; /* an array of 13 strings */

MonthNames[1] = “January”; /* String with 8 chars */

MonthNames[2] = “February”; /* String with 9 chars */

MonthNames[3] = “March”; /* String with 6 chars */

etc.

Exanple of array of strings#include<stdio.h>#include<conio.h>main(){

char name[3][10];int i;clrscr();printf(“\n enter three name”);for(i=0; i<3; i++){

scanf(“%s”,name[i]); printf(“\n you entered”);}for(i=0; i<3; i++){

printf(“\n %s”,name[i]);}

}

Output:

• enter three name harpreet kaur rajesh kumar jasmeet kaur

• you entered harpreet kaur rajesh kumar jasmeet kaur

Conclusion

Today we have learn about:what are strings?How we declare them?What are different methods for

reading and writing strings?Various function that are

performed on strings.How strings are stored in array.

Thanks