Strings in 'C' :

Strings in 'C' :

• String is a sequence of characters enclosed in double quotes and terminated by null character ("\0").
• Since 'C' language does not provides string data type array of character data type is used to store strings in 'C'. 
• While scanning string through scanf statement %s format specifier is used along with array name in which string to be stored. 
• Declaration syntax for string is char str_name[size];
• For example char str[5]; will store string of five characters in it. 
• Initialization : String can be initialized at the time of declaration itself or afterwards in a program.
• Example char str[5]="Hello";  Or char str[5]; str[]="Hello";
• String can be literal or variable.
• Literal means a constant.
• String which has assigned a value in a program itself can be called as string literal since it has predefined value. 
• But if we are accepting a string value from user then string can have any value thus it can be said as string variable.
• Consider following programs to illustrate strings :

1) Program using String as a literal

#include<stdio.h>

int main() 

{

 char str[50]="\nHello\n Welcome to strings in C\t bye...";

 printf("%s",str);

 return 0; 

}

Output :

Hello

Welcome to strings in C bye...

2) Program using string as a variable 

#include<stdio.h>

int main() 

{

 //declaring string variable 

 char str[10];

 printf("\n Enter String : ");

 scanf("%s",str);

 printf("\n You entered : %s",str);

 return 0; 

}

Output :

 Enter String : Hello

 You entered : Hello

3) Program to illustrate access of string character by character using array 

#include<stdio.h>

#include<string.h>

int main() 

{

 //declaring string variable 

 char str[30];

 int i;

 printf("\n Enter String : ");

 scanf("%s",str);

 printf("\n your string is :\n");

 //displaying string using array char by char

 for(i=0;i<strlen(str);i++)

 printf("%c",str[i]);

 return 0; 

}

Output :

 Enter String :Welcome

 your string is :

 Welcome

String Functions :

• 'C' language provides various built-in methods to work with strings. 
• These methods are called as string functions. 
• All these methods resides in a header file string.h. 
• Thus in order to use them we must include string.h in our program. 
• Some widely used string functions are as follow :

1) strcmp() : 

• As the name indicates these function is used to compare two strings. Syntax : strcmp(s1,s2); this function returns value 0 if both strings are same or equal. 
• It returns positive value if s1 is greater than s2 and negative value if s1 is less than s2. It uses ASCII value of each character in a string for comparison. 
• It compares string until they are same if not then returns from first non-matched character.

2) strncmp() :

• This function is similar to strcmp() but it only compares first n characters of two strings. 
• Syntax : strncmp(s1,s2,n);

3) strcat() : 

• This function is used for string concatenation or appending. 
• Syntax : strcat(s1,s2); It appends string2 to the string1. (Thus string1 will be changed.)

4) strncat() : 

• It is similar to strcat except that it appends only first 'n' characters of string2 to string1.
• Syntax : strncat(s1,s2,n);

5) strlen() : 

• This function returns length of string passed to it as an argument. That means it returns count of characters including spaces in a string. 
• Syntax : strlen(s);

6) strcpy() :  

• This function copies string2 to string1. If string 1 already holds some value then it replaces first n (n is length of string2) characters by string1 other characters remains same. 
• Syntax : strcpy(s1,s2);

7) strncpy() : 

• It similar to strcpy function except that it copies only first n characters of string2 to string1. 
• Syntax : strncpy(s1,s2,n);

8) strchr() : 

• This function shift string pointer to the first occurence of character c in a string.
•  Syntax : strchr(string,c);

9) strrchr() : 

• This function is similar to strchr except that pointer will be shifted to last occurence of character c in string. 
• Syntax : strrchr(string,c);

• Program to illustrate string functions :

#include<stdio.h>

#include<string.h>

int main() {

char s1[50],s2[50],str[50],r[50];

printf("\n Enter String1: ");

printf("%s",s1);

printf("\n Enter String2: ");

printf("%s",s2);

printf("\n String1: %s String2 : %s ",s1,s2);

//using string functions

strcmp(s1,s2)==0)

printf("\n Both strings are same");

else

printf("\n Both strings are not same");

printf("\n Lenght of string1 =%d",strlen(s1));

printf("\n concatening string1 and string 2 we get : %s",strcat(s1,s2));

printf("\n Appending 3 characters of string1 to string 2 we get : %s",strncat(s2,s1,3));

strcpy(str,s1);

printf("\n copying string1 to str : %s",str);

strncpy(r,s1,3);

printf("\n Copying first 3 characters of string1 to r : %s",r);

//finding first occurence 

printf("\n String after l in s2 is : %s",strchr(s2,'l'));

ntf("\n String after last 'e'in s2 is : %s",strrchr(s2,'e'));

if(strstr(s1,"Hello"))

printf("\n Hello is found in string1 ");

else

printf("\n Hello is not found in string1");

return 0;

}

Output : 

 Enter String1: HelloWorld 

 Enter String2: Welcomefriend

String1:HelloWorldString2: Welcomefriend 

 Both strings are not same

 Lenght of string1 =10

concatening string1 and string 2 we get : HelloWorldWelcomefriend
Appending 3 characters of string1 to string 2 we get : WelcomefriendHel

copyings tring1 to str: HelloWorldWelcomefriend

Copying first 3 characters of string1 to r : Hel

String after l in s2 is : lcomefriendHel
String after last 'e'in s2 is : el

Hello is found in string1

Array of Strings in 'C' language  :

• Basically a single string is itself an array of characters in 'C'. 
• Thus array of strings is a simply a two dimensional array of characters. 
• Syntax : char str_arr[rows][cols]; 
• For example  char str_arr[20][50];                  is a two dimensional array with 20 rows and 50 columns. 
• Thus we can store maximum 20 strings it in by using one string per row. 
• Let's see following program  :

#include<stdio.h>
int main()
{
 char str_arr[20][50];
 int n,i;
 printf("\n Enter how many strings: ");
 scanf("%d",&n);
 for(i=0;i<n;i++)
 {
 printf("\n Enter String%d : ",i);
 //storing string at row
 scanf("%s",str_arr[i]);
 }
 printf("\n Your strings are");
 for(i=0;i<n;i++)
 {
 printf("\n %s",str_arr[i]);
 }
return 0;
}

Output :
 Enter how many strings:
 Enter String0 : Hello
 Enter String1 : Welcome
 Enter String2 : Computer
 Enter String3 : Science
 Your strings are
 Hello
 Welcome
 Computer
 Science

Command line arguments in 'C' :

• Arguments which are accepted through command line are called command line arguments. 
• Command line arguments are generally passed to the main function. 
• In 'C' language when we accept command line arguments syntax for main function becomes

int main(int argc,char * argv)
{
  _____
  _____
}
Where argc stores count of arguments passed from command line and argv is a pointer pointing to array vector argv.

• Array vector argv stores actual arguments passed to main function. 
• Note that whatever arguments we pass to main function from command line are accepted as a string values. 
• Consider following programs

1) Program to accept and display command line arguments

#include<stdio.h>
#include<string.h>
int main(int argc,char * argv[])
{
int i,n=argc;
if(n==1)
printf("\n Arguments not given from command line...");
else
{
for(i=0;i<=n;i++)
printf("\n argument %d is : %s",i,argv[i]);
}
return 0;
}

Run command: ./a.out
Output 1:
Arguments not given from command line...

Run command : ./a.out Hello Welcome to command line

Output 2:
argument 0 is : ./a.out
argument 1 is : Hello
argument 2 is : Welcome
argument 3 is : to
argument 4 is : command
argument 5 is : line

2) Program  to compare two strings using command line arguments

#include<stdio.h>
#include<string.h>
int main(int argc,char * argv[])
{
int result=strcmp(argv[1],argv[2]);
if(result==0)
printf("\n Given strings are equal...");
else
printf("\n Given strings are different...");
return 0;
}

Run command : ./a.out Hello World
Output 1 :
Given strings are different...

Run command : ./a.out Hello Hello

Output 2:
Given strings are equal...

3) Program to calculate addition of two numbers using command line arguments

#include<stdio.h>
#include<stdlib.h>
int main(int argc,char * argv[])
{
int n1,n2;
//string to int conversion
n1=atoi(argv[1]);
n2=atoi(argv[2]);
printf("\n Addition of given numbers = %d",n1+n2);
return 0;
}

Run command: ./a.out 45 78

Output :

Addition of given numbers = 123

Note : atoi() is a function which converts asci value to integer form. Since arguments in argument vector are strings or we must convert them to integer form before operating on them.