C Strings

Strings

Strings are used for storing text/characters.

For example, "Hello World" is a string of characters.

Unlike many other programming languages, C does not have a String type to easily create string variables. Instead, you must use the char type and create an array of characters to make a string in C:

char greetings[] = "Hello World!";

Note that you have to use double quotes ("").

To output the string, you can use the printf() function together with the format specifier %s to tell C that we are now working with strings:

Example

char greetings[] = "Hello World!";
printf("%s", greetings);

Access Strings

Since strings are actually arrays in C, you can access a string by referring to its index number inside square brackets [].

This example prints the first character (0) in greetings:

Example

char greetings[] = "Hello World!";
printf("%c", greetings[0]);

Note: that we have to use the %c format specifier to print a single character.

Modify Strings

To change the value of a specific character in a string, refer to the index number, and use single quotes:

Example

  char greetings[] = "Hello World!";
greetings[0] = 'J';
  printf("%s", greetings);
// Outputs Jello World! instead of Hello
  World!

Loop Through a String

You can also loop through the characters of a string, using a for loop:

Example

char carName[] = "Volvo";
int i;

for (i = 0; i < 5; ++i) {

printf("%c\n", carName[i]);
}

And like we specified in the arrays loop chapter, you should use the sizeof formula (instead of manually write the size of the array in the loop condition (i < 5)) to make the loop more sustainable:

Example

char carName[] = "Volvo";
int length = sizeof(carName) /
sizeof(carName[0]);
int i;

for (i = 0; i < length; ++i) {

printf("%c\n", carName[i]);
}

Another Way Of Creating Strings

In the examples above, we used a "string literal" to create a string variable. This is the easiest way to create a string in C.

You should also note that you can create a string with a set of characters. This example will produce the same result as the example in the beginning of this page:

Example

char greetings[] = {'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd',
'!', '\0'};
printf("%s", greetings);

Note: Why do we include the \0 character at the end? This is known as the "null terminating character", and must be included when creating strings using this method. It tells C that this is the end of the string.

Differences

The difference between the two ways of creating strings, is that the first method is easier to write, and you do not have to include the \0 character, as C will do it for you.

You should note that the size of both arrays is the same: They both have 13 characters (space also counts as a character by the way), including the \0 character:

Example

char greetings[] = {'H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd',
'!', '\0'};
char greetings2[] = "Hello World!";

printf("%zu\n",
sizeof(greetings));   // Outputs 13
printf("%zu\n",
sizeof(greetings2));  // Outputs 13

Real-Life Example

Use strings to create a simple welcome message:

Example

  char message[] = "Good to see you,";
char fname[] = "John";

printf("%s
  %s!", message, fname);