chapter08

Chapter 8 - Strings

A string is a 1-D character array terminated by a null('\0')

\0 is null character.

Null Character-- Null character is used to denote string termination characters are stored in contiguous memory locations.

1. Creating strings

Strings in memory

A string is stored just like an array in the memory.

2. Create a string using "" and print its content using a loop.

Printing Strings

A string can be printed by character using printf and %c. But there is another convenient way to print a string.

char s[] = "Tushar";
printf("%s",s);

Taking input strings from a user

we can use %s with scanf to take string input.

char s[50];
scanf("%s",s);

3. Create a string, Take input from user and print the string.

Note-scanf can't be used in input multi word strings with spaces

gets() and puts()

gets() is a function which can be useed to recieve a multi-word string with spaces.

3. Create a string, Take input from user a multi-word string and print the string.

puts() can be used to output a string.

4. puts() example.

Declaring a string using pointers

char *ptr = "tushar";

this tells the compiler to store the string in memory and assigned address is stored in a char pointer.

Note

Once a string is defined using char st[]="Tushar", it can't be initialized to something else.

A string defined using pointers can be reinitialized.

ptr = "Tushar";

5. Reinitializing string.

Standard library functions for string

strlen()

Used to count the number of characters in the string excluding the null \0 character.

int length = strlen(st);

6. get the length of the string using standard library function..

7. Implement function that work same as strlen().

strcpy()

Used to copy the content of second string into first string passed to it.

strcpy(st2,st);

8. Copy string using strcopy() function.

strcat()

Used to concatenate two strings

9. Using strcat() function.

strcmp()

Used to compare two strings.
It returns: 0 if strings are equal
negative value: if first string mismatching character's ASCII value is not greater than second string's corresponding mismatching character.
otherwise it returns positive value.

strcmp("for","joke") -- positive value
strcmp("joke","for") -- negative value

sprintf and sscanf

A formatted string can be created with the sprintf() function. This is useful for building a string from another data types.

char a[] = "HEllo";
char s[100];
int n = 75;
sprintf(s,"%s %d",a,n);
printf("%s\n",s);

sscanf is used for scanning a string for values the function reads values from a string and stores them at the corresponding variable addresses.

Exercises

1. Write a program to take string as an input from an user using %c and %s. Confirm that the strings are equal.
2. Write your own strlen() function.
3. Write a function slice() to slice a string. It should change the original string such that it is now the sliced string.Take m and n as the start and ending position for slice.
4. Write your own version of strcpy() function from < string.h >
5. Write a program to encrypt a string by adding 1 to the ASCII value of its characters.
6. Write a program to decrypt the string encrypted using encrypte function in problem 5.
7. Write a program to count the occurence of a given character in a string.
8. Write a program to check whether a given character is present in a string or not.



A program which takes your password or any msg and display encrypted code if you want to decrypt it can decrypt it.