Strings in C

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Strings in C

A string in C is a one-dimensional array of char type, with the last character in the array being a "null character" represented by '\0'. Thus, a string in C can be defined as a null-terminated sequence of char type values.

Creating a String in C

Let us create a string "Hello". It comprises five char values. In C, the literal representation of a char type uses single quote symbols − such as 'H'. These five alphabets put inside single quotes, followed by a null character represented by '\0' are assigned to an array of char types. The size of the array is five characters plus the null character − six.

Example

char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

Initializing String Without Specifying Size

C lets you initialize an array without declaring the size, in which case the compiler automatically determines the array size.

Example

char greeting[] = {'H', 'e', 'l', 'l', 'o', '\0'};

The array created in the memory can be schematically shown as follows −

If the string is not terminated by "\0", it results in unpredictable behavior.

Note: The length of the string doesn’t include the null character. The library function strlen() returns the length of this string as 5.

Loop Through a String

You can loop through a string (character array) to access and manipulate each character of the string using the for loop or any other loop statements.

Example

In the following example, we are printing the characters of the string.

#include <stdio.h>
#include <string.h>

int main (){

   char greeting[] = {'H', 'e', 'l', 'l', 'o', '\0'};

   for (int i = 0; i < 5; i++) {
      printf("%c", greeting[i]);
   }

   return 0;
}

Output

It will produce the following output −

Hello

Printing a String (Using %s Format Specifier)

C provides a format specifier "%s" which is used to print a string when you're using functions like printf() or fprintf() functions.

Example

The "%s" specifier tells the function to iterate through the array, until it encounters the null terminator (\0) and printing each character. This effectively prints the entire string represented by the character array without having to use a loop.

#include <stdio.h>

int main (){

   char greeting[] = {'H', 'e', 'l', 'l', 'o', '\0'};
   printf("Greeting message: %s\n", greeting );

   return 0;
}

Output

It will produce the following output −

Greeting message: Hello

You can declare an oversized array and assign less number of characters, to which the C compiler has no issues. However, if the size is less than the characters in the initialization, you may get garbage values in the output.

char greeting[3] = {'H', 'e', 'l', 'l', 'o', '\0'};
printf("%s", greeting);

Constructing a String using Double Quotes

Instead of constructing a char array of individual char values in single quotation marks, and using "\0" as the last element, C lets you construct a string by enclosing the characters within double quotation marks. This method of initializing a string is more convenient, as the compiler automatically adds "\0" as the last character.

Example

#include <stdio.h>

int main() {
  // Creating string
  char greeting[] = "Hello World";

  // Printing string
  printf("%s\n", greeting);

  return 0;
}

Output

It will produce the following output −

Hello World

String Input Using scanf()

Declaring a null-terminated string causes difficulty if you want to ask the user to input a string. You can accept one character at a time to store in each subscript of an array, with the help of a for loop −

Syntax

for(i = 0; i < 6; i++){
   scanf("%c", &greeting[i]);
}
greeting[i] = '\0';

Example

In the following example, you can input a string using scanf() function, after inputting the specific characters (5 in the following example), we are assigning null ('\0') to terminate the string.

printf("Starting typing... ");

for (i = 0; i < 5; i++) {
  scanf("%c", &greeting[i]);
}

// Assign NULL manually
greeting[i] = '\0';

// Printing the string
printf("Value of greeting: %s\n", greeting);

Output

Run the code and check its output −

Starting typing... Hello
Value of greeting: Hello

Example

It is not possible to input "\0" (the null string) because it is a non-printable character. To overcome this, the "%s" format specifier is used in the scanf() statement −

#include <stdio.h>
#include <string.h>

int main (){

   char greeting[10];

   printf("Enter a string:\n");
   scanf("%s", greeting);

   printf("You entered: \n");
   printf("%s", greeting);

   return 0;
}

Output

Run the code and check its output −

Enter a string:
Hello
You entered:
Hello

Note: If the size of the array is less than the length of the input string, then it may result in situations such as garbage, data corruption, etc.

String Input with Whitespace

scanf("%s") reads characters until it encounters a whitespace (space, tab, newline, etc.) or EOF. So, if you try to input a string with multiple words (separated by whitespaces), then the C program would accept characters before the first whitespace as the input to the string.

Example

Take a look at the following example −

#include <stdio.h>
#include <string.h>

int main (){

   char greeting[20];

   printf("Enter a string:\n");
   scanf("%s", greeting);

   printf("You entered: \n");
   printf("%s", greeting);

   return 0;
}

Output

Run the code and check its output −

Enter a string:
Hello World!

You entered:
Hello

String Input Using gets() and fgets() Functions

To accept a string input with whitespaces in between, we should use the gets() function. It is called an unformatted console input function, defined in the "stdio.h" header file.

Example: String Input Using gets() Function

Take a look at the following example −

#include <stdio.h>
#include <string.h>

int main(){

   char name[20];

   printf("Enter a name:\n");
   gets(name);

   printf("You entered: \n");
   printf("%s", name);

   return 0;
}

Output

Run the code and check its output −

Enter a name:
Sachin Tendulkar

You entered: 
Sachin Tendulkar

In newer versions of C, gets() has been deprecated. It is potentially a dangerous function because it doesn’t perform bound checks and may result in buffer overflow.

Instead, it is advised to use the fgets() function.

fgets(char arr[], size, stream);

The fgets() function can be used to accept input from any input stream, such as stdin (keyboard) or FILE (file stream).

Example: String Input Using fgets() Function

The following program uses fgets() and accepts multiword input from the user.

#include <stdio.h>
#include <string.h>

int main(){

   char name[20];

   printf("Enter a name:\n");
   fgets(name, sizeof(name), stdin);

   printf("You entered: \n");
   printf("%s", name);

   return 0;
}

Output

Run the code and check its output −

Enter a name:
Virat Kohli

You entered: 
Virat Kohli

Example: String Input Using scanf("%[^\n]s")

You may also use scanf("%[^\n]s") as an alternative. It reads the characters until a newline character ("\n") is encountered.

#include <stdio.h>
#include <string.h>

int main (){

   char name[20];

   printf("Enter a name: \n");
   scanf("%[^\n]s", name);

   printf("You entered \n");
   printf("%s", name);

   return 0;
}

Output

Run the code and check its output −

Enter a name: 
Zaheer Khan

You entered 
Zaheer Khan

Printing String Using puts() and fputs() Functions

We have been using printf() function with %s specifier to print a string. We can also use puts() function (deprecated in C11 and C17 versions) or fputs() function as an alternative.

Example

Take a look at the following example −

#include <stdio.h>
#include <string.h>

int main (){

   char name[20] = "Rakesh Sharma";

   printf("With puts(): \n");
   puts(name);

   printf("With fputs(): \n");
   fputs(name, stdout);

   return 0;
}

Output

Run the code and check its output −

With puts(): 
Harbhajan Singh

With fputs(): 
Harbhajan Singh