1. Strings in C Array of characters is called a string.
A string is terminated by a null character \0.
Ex: “C String”
Here “C string” is a string. When compiler encounters a string, it appends \0(null character) at the end of the string. C S t r i n g \0

2. Declaration of strings
Strings are declared in a similar manner as arrays. Only difference is that, strings are of char data type. char s[5];

3. Initialization of strings
In C, string can be initialized in a number of different ways.
For convenience and ease, both initialization and declaration are done in the same step.
char c[] = "abcd";
OR,
char c[50] = "abcd";
char c[] = {'a', 'b', 'c', 'd', '\0'};
char c[5] = {'a', 'b', 'c', 'd', '\0'}; a b c d \0

4. Reading Strings from user
Use scanf() to read a string like any other data type.
The scanf() function only takes the first entered word. The function terminates when it encounters a space.
Reading words from the user
char c[20];
scanf(“%s”,c);

5. Using scanf() to read a string
C program to illustrate how to read string from terminal. Sample output: Enter name: Mani Ratnam Your name is Mani
void main() {
char name[20];
printf("Enter name: ");
scanf("%s",name);
printf("Your name is %s",name); }

6. Using getchar() to read a line of text
C program to read a line of text characters.
Sample output:
Enter name: Mani Ratnam
Your name : Mani Ratnam
void main() {
char name[30], ch;
int i=0;
printf("Enter name: ");
while(ch!=‘\n’)
ch=getchar();
name[i]= ch;
i++; }
name[i]=‘\0’;
printf("Your name : %s",name);
Using the function getchar(), ch gets a single character from the user each time.
This process is repeated until the user enters return (enter key). Finally, the null character is inserted at the end to make it a string.

7. Using gets() and puts()to read a line of text
C program to read a line of text characters.
Sample output:
Enter name: Mani Ratnam
Your name : Mani Ratnam
void main() {
char name[30];
printf("Enter name: ");
gets(name);
printf(“Your name: ");
puts(name); }
Using the function gets(), a series of characters are received until user press enter.
The compiler insert the null character at the end to make it a string.

8. Passing string to a function
#include <stdio.h>
void displayString(char str[]);
void main() {
char str[50];
printf("Enter string: ");
gets(str);
displayString(str); // Passing string c to function. }
void displayString(char str[])
printf("String Output: ");
puts(str);
Strings are just char arrays. So, they can be passed to a function in a similar manner as arrays.

9. String Handling Functions
There are various string operations you can perform manually like: finding the length of a string, concatenating (joining) two strings etc.
But, for programmer's ease, many of these library functions are already defined under the header file <string.h>

10. String Handling Functions
String Length Function

11. strlen(string) #include <stdio.h> #include <string.h>
It returns the length of the string without including end character (terminating char ‘\0’).
#include <stdio.h>
#include <string.h>
void main() {
char str1[20] = "Book";
printf("Length of string str1: %d", strlen(str1)); }

12. Length of the string without using built in function
#include <stdio.h>
void main() {
char string[50];
int i, length = 0;
printf("Enter a string \n");
gets(string);
/* keep going through each character of the string till its end */
for (i = 0; string[i] != '\0'; i++)
length++; }
printf(“The length of %s = %d\n", string, length);

13. strlen vs sizeof strlen returns you the length of the string stored in array,
sizeof returns the total allocated size assigned to the array.

14. strnlen(string , maxlength)
It returns length of the string if it is less than the value specified for maxlen (maximum length) otherwise it returns maxlen value.
#include <stdio.h>
#include <string.h>
void main() {
char str1[20] = “Record Book";
printf("Length of string str1 when maxlen is 30: %d", strnlen(str1, 30));
printf("Length of string str1 when maxlen is 10: %d", strnlen(str1, 10)); }
Output: Length of string str1 when maxlen is 30: 11 Length of string str1 when maxlen is 10: 10

15. String Handling Functions
String Comparing Function

16. strcmp(string1, string2)
If string1 < string2 OR string1 is a substring of string2 then it would result in a negative value. If string1 > string2 then it would return positive value. If string1 == string2 then you would get 0(zero) when you use this function for compare strings.

17. #include <stdio.h>
#include <string.h>
void main() {
char s1[20] = “Record";
char s2[20] = “Record Book";
if (strcmp(s1,s2)==0)
printf("string 1 and string 2 are equal"); }
else
printf("string 1 and 2 are different");

18. /*Program to compare Strings without using built in function */
 void main() {
   char str1[30], str2[30];
   int i;
    printf("\nEnter two strings :");
   gets(str1);
   gets(str2);
    i = 0;
   while (str1[i] == str2[i] && str1[i] != '\0')
     {
 i++; }
   if (str1[i] > str2[i])
      printf("str1 > str2");
   else if (str1[i] < str2[i])
      printf("str1 < str2");
   else
      printf("str1 = str2");
  }
/*Program to compare Strings without using built in function */

19. strncmp(string1, string2, n)
It compares both the string till n characters or in other words it compares first n characters of both the strings.
void main()
{ char s1[20] = “Record Book";
char s2[20] = “Record work";
/* below it is comparing first 6 characters of s1 and s2*/
if (strncmp(s1, s2, 6) ==0)
{ printf("string 1 and string 2 are equal");
else
printf("string 1 and 2 are different"); }
Output:
string1 and string 2 are equal

20. String Handling Functions
String Concatenation Function

21. strcat(string1, string2)
It concatenates two strings and returns the concatenated string. That is, it attaches the string 2 to the RHS of the string 1.
int main() {
char s1[10] = "Hello"; char s2[10] = "World";
strcat(s1,s2);
printf("string after concatenation: %s", s1);
return 0; }
Output : string after concatenation: HelloWorld

22. /*Program to concatenate Strings without using built in function */
void main(void)
{ char str1[25],str2[25];
int i=0, j=0;
printf("\nEnter First String:");
gets(str1);
printf("\nEnter Second String:");
gets(str2);
while(str1[i]!='\0')
i++;
while(str2[j]!='\0') {
str1[i]=str2[j];
j++; }
str1[i]='\0';
printf("\nConcatenated String is %s",str1);
/*Program to concatenate Strings without using built in function */

23. strncat(string1, string2, n)
It concatenates n characters of str2 to string str1.
A terminator char (‘\0’) will always be appended at the end of the concatenated string.
int main() {
char s1[10] = "Hello";
char s2[10] = “1234";
strncat(s1,s2, 3);
printf("Concatenation using strncat: %s", s1);
return 0; }
Output:
Concatenation using strncat: Hello123

24. String Handling Functions
String Copy Function

25. strcpy(string1, string2)
It copies the string str2 into string str1, including the end character (terminator char ‘\0’).
void main() {
char s1[30] = “hi";
char s2[30] = “programmer";
/* this function has copied s2 into s1*/
strcpy(s1,s2);
printf("String s1 is: %s", s1); }
Output:
String s1 is: programmer

26. /*Program to copy Strings without using built in function */
void main() {
char s1[100], s2[100], i;
printf("Enter string s1: ");
scanf("%s",s1);
for(i = 0; s1[i] != '\0'; ++i)
s2[i] = s1[i]; }
s2[i] = '\0';
printf("String s2: %s", s2);
/*Program to copy Strings without using built in function */

27. strncpy(string1, string2, n)
Case1: If length of str2 > n then it just copies first n characters of str2 into str1. Case2: If length of str2 < n then it copies all the characters of str2 into str1 and appends several terminator chars(‘\0’) to accumulate the length of str1 to make it n.
void main() {
char first[30] = “hello”;
char second[30] =“Amrita”;
/* this function has copied first 10 chars of s2 into s1*/
strncpy(s1,s2, 5);
printf("String s1 is: %s", s1); }
Output:
String s1 is:Amrit