Programming Strings: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.
How to declare a string?
char s[5];
Here, we have declared a string of 5 characters.
How to initialize strings?
You can initialize strings in a number of ways.
char c[] = "abcd";
char c[50] = "abcd";
char c[] = {'a', 'b', 'c', 'd', '\0'};
char c[5] = {'a', 'b', 'c', 'd', '\0'};
String Initialization in C
Assigning Values to Strings
Arrays and strings are second-class citizens in C; they do not support the assignment operator once it is
declared. For example,
char c[100];
c = "C programming"; // Error! array type is not assignable. Use the strcpy() function to copy the string instead.
Read String from the user
You can use the scanf() function to read a string.
The scanf() function reads the sequence of characters until it encounters whitespace (space, newline, tab, etc.).
Example 1: scanf() to read a string
#include <stdio.h>
int main()
{
char name[20];
printf("Enter name: ");
scanf("%s", name);
printf("Your name is %s.", name);
return 0;
}
Output
Enter name: Dennis Ritchie
Your name is Dennis.
Even though Dennis Ritchie was entered in the above program, only "Dennis" was stored in the name string.
It's because there was a space after Dennis.
Also notice that we have used the code name instead of &name with scanf().
How to read a line of text?
You can use the fgets() function to read a line of string. And, you can use puts() to display the string.
Example 2: fgets() and puts()
#include <stdio.h>
int main()
{
char name[30];
printf("Enter name: ");
fgets(name, sizeof(name), stdin); // read string
printf("Name: ");
puts(name); // display string
return 0;
}
Output
Enter name: Tom Hanks
Name: Tom Hanks
Passing Strings to Functions
Strings can be passed to a function in a similar way as arrays.
Example 3: Passing string to a Function
#include <stdio.h>
void displayString(char str[]);
int main()
{
char str[50];
printf("Enter string: ");
fgets(str, sizeof(str), stdin);
displayString(str); // Passing string to a function.
return 0;
}
void displayString(char str[])
{
printf("String Output: ");
puts(str);
}
Commonly Used String Functions
strlen() - calculates the length of a string
strcpy() - copies a string to another
strcmp() - compares two strings
strcat() - concatenates two strings
strlen():
The strlen() function takes a string as an argument and returns its length. The returned value is of
type size_t (an 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.
strcat()
The function definition of strcat() is:
char *strcat(char *destination, const char *source)
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.It is defined in the string.h header file.
Example: C strcat() function
#include <stdio.h>
#include <string.h>
int main() {
char str1[100] = "This is ", str2[] = "programiz.com";
// concatenates str1 and str2
// the resultant string is stored in str1.
strcat(str1, str2);
puts(str1);
puts(str2);
return 0;
}
Output
This is programiz.com
programiz.com
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 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;
}
Run Code
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 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
>0 if the first non-matching character in str1 is greater (in ASCII) than that of str2 .
<0 if the first non-matching character in str1 is lower (in ASCII) than that of str2 .
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.
