In C programming, a string is a sequence of characters terminated with a null character \0.
For example:
char c[ ] = "c string";
When the compiler encounters a sequence of characters enclosed in the double quotation marks, it appends a null character \0 at the end by default.
String:
- A string is a sequence of characters that treated as a single data item.
- The string is defined between double quotation mark.
Example: “ I teach C language”
List of strings operation:
• The operations performed on strings are follows:
- Reading and Writing strings
- Combining string together
- Comparing two strings
- Copying one string to another
Declaration and initialization of string:
• C does not support string as data type, so to declare string variable
character array is used.
• Declaration of String:
char string_name[size];
Here the size determines the number of character in string_name.
• Example :
char city[10];
When the compiler assigns a character string to character array, it
automatically supplies null character(‘\0’) at the end of string.
Therefore the size should be equal to maximum number of characters
in string plus one.
• Initialization of string:
char city[9] = ’’NEW YORK”;
char city[9] = {‘N’,’E’,’W’,’ ’,’Y’,’O’,’R’,’K’,’\0’};
char city[]=”NEW YORK”;
- We can also declare the size larger than the string size in the initialize. char city[20]=”NEW YORK”; We cannot declare the size smaller than the string size in the initialize. char city[5]=”NEW YORK”; this will result in a compile time error.
- We cannot separate the initialization from declaration. char city[9]; city = “NEW YORK”;
it is not allowed.
- Declaring and initializing string variables
char string_name[size];
- Reading strings from terminal
scanf(“%s”, string_name);
gets(string_name);
getchar();
- Printing strings to terminal
printf (“%s”, string_name);
puts(string_name);
putchar(char_name);
Reading strings from the user:
scanf() function:
- Input function scanf is used with %s format specification to read string.
scanf(“%s”,city);
- The problem with scan function is that it terminates reading on the first white space it finds.
- A white space includes blanks, tabs, carriage returns and new lines.
- Example : If the NEW YORK is input then only “NEW” will be read, because the blank space after the word NEW will terminate the reading of string.
- We can also specify the field width using the form %ws in the scanf statement for reading a specified number of characters from the input string.
getchar and gets functions :
getchar()
- getchar is the function to read a single character from the terminal.
- The reading is terminated when the new line character (‘\n’) is entered and the null character is then inserted at the end of the string. char ch; ch = getchar( );
- getchar function has no parameters
gets()
- gets is the function to read characters into string from the terminal.
- gets is the library function and available in
header file.
- The gets function called as under : gets(str);
where str is the string variable.
The reading is terminated when the new line character (‘\n’) is encountered and the null character is then inserted at the end of the string.
gets function has one parameter.
Writing strings from terminal
printf function:
• Output function printf is used with %s format specification to write
string.
Example :
printf(“%s”, name);
putchar and puts functions :
putchar
- putchar is the function to print the values of character variables.
- It takes the following form : char ch = ‘A’; putchar(ch)
- The function putchar has one parameter.
- We can use this function repeatedly to print a string of characters stored in array using a loop.
- Example :
char name = “VINAYAK INFOTECH”;
for (i=0; i<=5; i++)
{
putchar(name[i]);
}
puts functions
- puts is the function to print the values of string variables.
- puts is the library function and available in
header file. The puts function called as under : puts(str); where str is the string variable. puts function has one parameter. Example :
- This example read a line of text from the keyboard and displays it on the screen.
String Handling Functions or Built-in String
Functions or String Manipulation Functions:
Function Work of Function
- strlen() computes string's length
- strcpy() copies a string to another
- strcat() concatenates(joins) two strings
- strcmp() compares two strings
C strlen()
The strlen() function calculates the length of a given string.
- The strlen() function takes a string as an argument and returns its length. The returned value is of type size_t (the unsigned integer type).
- It is defined in the <string.h> header file.
- Example: C strlen() function
#include <stdio.h>
#include <string.h>
int main()
{
char a[20]="Program";
char b[20]={'P','r','o','g','r','a','m','\0'};
// using the %zu format specifier to print size_t
printf("Length of string a = %zu \n",strlen(a));
printf("Length of string b = %zu \n",strlen(b));
return 0;
}
Output:
Length of string a = 7
Length of string b = 7
Note that the strlen() function doesn't count the null character \0 while calculating the length.
C strcpy()
- The function prototype of strcpy() is:
char* strcpy(char* destination, const char* source);
- The strcpy() function copies the string pointed by source (including the null character) to the destination.
- The strcpy() function also returns the copied string.
- The strcpy() function is defined in the string.h header file.
Example: C strcpy()
#include <stdio.h>
#include <string.h>
int main()
{
char str1[20] = "C programming";
char str2[20];
// copying str1 to str2 strcpy(str2, str1);
puts(str2);
// C programming return 0;
}
Output:
C programming
Note: When you use strcpy(), the size of the destination string should be large enough to store the copied string. Otherwise, it may result in undefined behavior.
C strcat()
In C programming, the strcat() function contcatenates (joins) two strings.
The function definition of strcat() is:
char *strcat(char *destination, const char *source)
It is defined in the string.h header file.
strcat() arguments:
As you can see, the strcat() function takes two arguments:
destination - destination string
source - source string
The strcat() function concatenates the destination string and the source string, and the result is stored in the destination string.
Example: C strcat() function
#include <stdio.h>
#include <string.h>
int main()
{
char str1[100] = "This is ", str2[] = "quickcodings.blogspot.com";
// concatenates str1 and str2
// the resultant string is stored in str1.
strcat(str1, str2);
puts(str1);
puts(str2);
return 0;
}
Output:
This is quickcodings.blogspot.com
quickcodings.blogspot.com
Note: When we use strcat(), the size of the destination string should be large enough to store the resultant string. If not, we will get the segmentation fault error.
C strcmp()
The strcmp() compares two strings character by character. If the strings are equal, the function returns 0.
C strcmp() Prototype
The function prototype of strcmp() is:
int strcmp (const char* str1, const char* str2);
strcmp() Parameters
The function takes two parameters:
- str1 - a string
- str2 - a string
Return Value from strcmp()
Return Value Remarks
- 0 if strings are equal
- non-zero if strings are not equal
The strcmp() function is defined in the string.h header file.
Example: C strcmp() function
#include <stdio.h>
#include <string.h>
int main()
{
char str1[] = "abcd", str2[] = "abCd", str3[] = "abcd"; int result;
// comparing strings str1 and str2 result = strcmp(str1, str2);
printf("strcmp(str1, str2) = %d\n", result);
// comparing strings str1 and str3 result = strcmp(str1, str3);
printf("strcmp(str1, str3) = %d\n", result);
return 0;
}
Output:
strcmp(str1, str2) = 1
strcmp(str1, str3) = 0
In the program,
- strings str1 and str2 are not equal.
- Hence, the result is a non-zero integer. strings str1 and str3 are equal. Hence, the result is 0.
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