Lesson 10.1. Strings in C


A string is a particular format of array intended to store alphanumeric characters, i.e. text. A classic example of a string is the first parameter of the printf() function:


In the above example, "Hello!" is a string.


A string is a special case of character arrays, whose syntax they share. The following example declares :

char text[10];

In this section on strings, we will use the standard string.h library which contains the basic functions for string processing:

#include <string.h>


A string being an array, it is possible to initialize it at the declaration character by character :

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

Note by the way that the last character is '\0' which is the first character of the ASCII table.

However, there is a more user-friendly way to initialize a string in the :

char text[] = "Hello!";

In C, double quotes mark the beginning and end of a string (as in the printf() function). Be careful not to confuse this syntax with single quotes which are intended to specify a single character:

// Single character
char c = 'L'; 

// String
char text[] = "My text";


Here is an example of how to create a string:

// Declare and initialize a string
char text[] = "This is a string.";

// Display the string
printf ("%s\n", text);

// Display string and array sizes
printf ("Array size  : %ld octets\n", sizeof(text));
printf ("String size : %ld caractères\n", strlen(text));

// Display the first cells of the array
printf ("text[0] =  %c\n", text[0]);
printf ("text[1] =  %c\n", text[1]);
printf ("text[2] =  %c\n", text[2]);
printf ("text[3] =  %c\n", text[3]);

Some comments about this example:


Exercise 1

Write a program that declares a string url containing the text https://lucidar.me. Display:

String content : https://lucidar.me
Array size     : 19 octets
String size    : 18 caractères

Exercise 2

We provide the following string declaration:

char str[] = "string";

Using a loop, iterate through the characters of the string one by one and display them as :

Use sizeof() to determine the length of the array in the loop. Here is the expected output from this exercise:

str[0]  = 's'   = 115   = 0x73
str[1]  = 't'   = 116   = 0x74
str[2]  = 'r'   = 114   = 0x72
str[3]  = 'i'   = 105   = 0x69
str[4]  = 'n'   = 110   = 0x6E
str[5]  = 'g'   = 103   = 0x67
str[6]  = ''    =  0    = 0x00


In C, a string ...

Check Bravo! In C, a string is a special case of alphanumeric character array Try again...

Which library contains the elementary functions for strings?

Check Bravo! string.h is a very popular library. Try again...

What the following code displays:

char str[100] ="Cuckoo";
printf ("sizeof = %ld", sizeof(str));
Check Bravo! This is the size of the array that is displayed with sizeof(). Try again...

Qu'affiche le code suivant :

char str[100] ="Cuckoo";
printf ("strlen = %ld", strlen(str));
Check Bravo! This is the size of the string that is displayed with strlen(). Try again...

See also

Last update : 01/13/2023