Strings are arrays of characters that end with a null character. They can be declared using character arrays or pointers. Strings passed to functions are passed by reference as pointers. Common string functions include strlen to get length, strcmp to compare strings, strcpy to copy one string to another, and strcat to concatenate strings. Strtok breaks a string into tokens delimited by a specified character.

1. Strings and Pointers

2. STRING
 String is a one dimensional array of characters.
 Start with index 0 and end with null character i.e. 0.
 A string may include letter,digits and special
characters(+,-,*,/,$).

3. Declaration
 A string can be declared in two ways:-
1. Character array-
char color[]=“blue”;
2. Using pointer variable-
const char *colorptr[]=“blue”;

4.  The first declaration creates a five-element array color
containing the characters ‘b’ , ‘l’ , ‘u’ , ‘e’ and ‘0’.
 The second declaration creates pointer variable colorptr
that points to the character ‘b’ in the string “blue”
somewhere in memory.
 The declaration char color[]=“blue”; could also be
written as:
char color[]={‘b’ , ‘l’ , ‘u’ , ‘e’ , ‘0’};

5. Passing Strings
 Just as we can pass other kinds of arrays to functions, we
can do so with strings.
 Below is the definition of a function that prints a label and
a call to that function:

6.  Since label is a character array, and the function
PrintLabel() expects a character array.
 However, if we have a pointer to the character array label,
as in:
char *labelPtr = label;
 Then we can also pass the pointer to the function, as in:
PrintLabel(labelPtr);
 The results are the same.
Why??

7.  When we declare an array as the parameter to a function, we really
just get a pointer. Plus, arrays are always automatically passed by
reference (e.g., a pointer is passed).
 So, PrintLabel() could have been written in two ways:
void PrintLabel(char the_label[])
{
printf("Label: %sn", the_label);
}
OR
void PrintLabel(char *the_label)
{
printf("Label: %sn", the_label);
}

8. Various String Manipulation Functions
 The library <cstring> has several common functions for
dealing with strings. The following four are the most useful
ones that we'll discuss:
 strlen(str) :-Returns the number characters in the
string, not including the nul character.

9.  Output of this program is:

10. strcmp(str1, str2):- This function takes two strings and
compares them. If the strings are equal, it returns 0. If the
first is greater than the 2nd, then it returns some value
greater than 0. If the first is less than the 2nd, then it
returns some value less than 0.

11. Output of this program is :-

12.  The ordering for strings is lexical order based on the ASCII
value of characters. Remember that the ASCII value
of 'A' and 'a' (i.e., upper/lowercase) are not the same.
 An easy way to remember how to use strcmp() to compare
2 strings (let's say a and b) is to use the following
mnemonics:
Want…. Use…
a==b strcmp(a, b) == 0
a<b strcmp(a, b) < 0
a>=b strcmp(a, b) >= 0

13.  strcpy(dest, source) :-
Copies the contents of source into dest, as in:

14. Output of this program is:-

15. Now, the string str1 contains the following:
-------------------------------------------
| s | e | c | o | n | d | 0 | u | e | 0 |
-------------------------------------------
and the word "initvalue" has been overwritten.
Note that it is the first nul character (0) that determines the
end of string.
When using strcpy(), make sure the destination is big enough
to hold new string.
 Aside: An easy way to remember that the destination comes
first is because the order is the same as for assignment, e.g:
dest = source
 Also, strcpy() returns the destination string, but that return
value is often ignored.

16.  strcat(dest, source) :-
Copies the contents of source onto the end of dest,as in:

17. Output of this program is :-

18. Strtok(char s1,const char s2) :-
 A sequence of calls to strtok breaks string s1 into “tokens” –
logical pieces such as words in a line of text- delimited by
characters contained in string s2(delimiter).
 The first call contains s1 as the first argument, and subsequent
calls to continue tokenizing the same string contain NULL as
the first argument.
 A pointer to the current token is returned by each call. If there
are no more tokens when the function is called NULL is
returned.

19. Consider following program :-

20. Output of this program is :-