Category: 11. Strings

The C language identifies a character set that comprises English alphabets upper and lowercase (A to Z as well as “a” to “z”), digits 0 to 9, and certain other symbols called “special characters” with a certain meaning attached to them.

While many of the characters in the special symbol category are defined as operators, certain combinations of characters also have a special meaning attached to them. For example, “\n” is known as the newline character. Such combinations are called escape sequences.

In C language, quotation marks too have a special meaning. Double quotes are used for strings, while characters are enclosed inside single quotes. Read this chapter to learn more about the other special characters used in C programs.

Parentheses ()

Parentheses are especially used to group one or more operands in an expression and control the order of operations in a statement.

A part of the expression embedded inside parentheses has a higher order of precedence.

Example

int a =2, b =3, c =4;int d =(a + b)* c;

Braces { }

Braces are especially used to define blocks of code, such as function bodies and loops. They are also used to initialize arrays and struct variables.

Examples

Braces in function definition −

intadd(int a,int b){int sum = a + b;return sum;}

Braces in array initialization −

int arr[5]={1,2,3,4,5};

Braces in struct variable −

structbook{char title[10];double price;int pages;};structbook b1;structbook b1 ={"Learn C",675.50,325};

Square Brackets [ ]

Square brackets are used to declare arrays and access elements of an array with the subscript index.

Example

For example, to define an array of integers and access its third element, you would use square brackets −

int arr[5]={1,2,3,4,5};int third = arr[2];

Asterisk (*)

Apart from its use as a multiplication operator, the asterisk symbol (*) is also used to declare a pointer variable and dereference it to obtain the value of the target variable.

Example

For example, to define a pointer to an integer and access the value it points to, you would use an asterisk −

int num =10;int*ptr =#printf("*d",*ptr);

Ampersand (&)

The ampersand (&) symbol is used as the address-of operator. It returns the address of a variable.

Example

For example, to get the address of an integer variable, you would use an ampersand −

int num =10;int*ptr =#

Comma (,)

The comma is used as a separator between a statement or a function call.

Example

int a =1, b =2, c =3;

Semicolon (;)

As a primary syntax rule in C, the semicolon indicates the end of a statement in a C program.

Example

printf("Hello, world!");

Dot (.)

The dot symbol (.) is used to access the members of a structure or a union.

Example

structbook b1 ={"Learn C",675.50,325};printf("Title: %s\n", b1.title);printf("Price: %lf\n", b1.price);printf("No of Pages: %d\n", b1.pages);

Arrow ()

The arrow symbol () is used to access the members of a structure or a union through a pointer.

Example

structbook b1 ={"Learn C",675.50,325};structbook*strptr;
strptr =&b1;printf("Title: %s\n", strptr->title);printf("Price: %lf\n", strptr->price);printf("No of Pages: %d\n", strptr->pages);

In C, characters and strings are stored differently. A character array stores a sequence of characters, like text. We use single quotes (‘ ‘) to define a single character (e.g., ‘A’) and double quotes (” “) to define a string or a character array (e.g., “A”, “Hello”).

The main difference is that a single character is stored as its ASCII value, while a string is stored as a sequence of characters ending with a null terminator (\0). In this chapter, we will see single and double quoted character arrays.

Understanding Chracter Arrays in C

A character array is a collection of characters stored in consecutive memory locations, which means each character occupies the next memory slot one after the another. In C, we use character arrays to represent strings, which are enclosed in double quotes and a null terminator (\0) is added at the end of each string to mark its end.

Example of a Character Array

In this example, we declare a character array str[] with 6 elements and print it using %s. Each character is stored one after the other in memory, so the program prints them one by one until it reaches the null terminator \0.

#include <stdio.h>intmain(){char str[]="Hello";// Creating a character array of 6 chractersprintf("%s", str);// Printing the stringreturn0;}

Below you can see the output of the above program, which displays the string stored in the character array.

Hello

Single Quotes in C

Single quotes (‘ ‘) in C are used to represent single character. We can also use them to create a character array by listing characters one by one inside braces {}. Each character is stored internally as its ASCII value.

For example, ‘A’ represents the character A, but in memory it is stored as the number 65, which is the ASCII value of A.

Note that we cannot use single quotes to store multiple characters together like ‘Hi’ because that will cause an error.

Example of Single Quoted Character Array

Below is an example showing a character array using single quotes. Here, we declare a character array arr to store the characters ‘H’, ‘i’, and ‘!’. We then print each character one by one in a loop.

#include <stdio.h>intmain(){char arr[]={'H','i','!'};// Creating a single-quoted character arrayint i;for(i =0; i <3; i++){printf("%c ", arr[i]);// Prints each character}return0;}

Below is the output of the above program, which displays each character of the array one by one.

H i !

Double Quotes in C

Double quotes (” “) in C are used to represent string literals, which are stored as character arrays. A string in C always ends with a null character (\0) so that the program knows where the string ends.

For example, “A” may look like a single character, but in memory, it is stored as two characters: ‘A’ followed by ‘\0’.

Note: Unlike single quotes, double quotes can store multiple characters as a string.

Example of Double Quoted Character Array

Below is an example showing the use of double quotes. Here, we define a string str with the value “Hi”. So, “Hi” is stored as three characters: ‘H’, ‘i’, and the null terminator ‘\0’. That is why the size of the array becomes 3.

#include <stdio.h>intmain(){// storing the string "Hi" in a character array (includes '\0' automatically)char str[]="Hi";printf("String: %s\n", str);printf("Size of str: %lu\n",sizeof(str));return0;}

Following is the output of the above program, which displays the given string and also shows the size of the array (including the null terminator) −

String: Hi
Size of str: 3

Common Mistakes

When working with characters and strings in C, it’s easy to get confused when to use single quotes (‘ ‘) and double quotes (” “). Here are two common mistakes to avoid −

• Using double quotes for a single character −

char c ="A";// Wrong: "A" is a string (character array), not a single characterchar c ='A';// Correct: 'A' is a single character

Always use single quotes when you want to store just one character.

• Using single quotes for strings −

char str[]='Hello';// Wrong: single quotes can only hold one characterchar str[]="Hello";// Correct: double quotes are used for strings

Always use double quotes when you want to store multiple characters (a string).

Difference between Single and Double Quotes in C

The following table shows the key differences between single quotes and double quotes in C −

Conclusion

In this chapter, we learned that single quotes are used to store a single character as its ASCII value, while double quotes store multiple characters as a string ending with a null terminator. We also looked at their differences in character arrays.

In C programming language, a string is an array of character sequences terminated by NULL, it is a one-dimensional array of characters. And, the array of strings is an array of strings (character array).

What is an Array of Strings in C?

Thus, an array of strings can be defined as –

An array of strings is a two-dimensional array of character-type arrays where each character array (string) is null-terminated.

To declare a string, we use the statement −

char string[]={'H','e','l','l','o','\0'};
Or
char string ="Hello";

Declare and Initialize an Array of Strings

To declare an array of strings, you need to declare a two-dimensional array of character types, where the first subscript is the total number of strings and the second subscript is the maximum size of each string.

To initialize an array of strings, you need to provide the multiple strings inside the double quotes separated by the commas.

Syntax

To construct an array of strings, the following syntax is used −

char strings [no_of_strings][max_size_of_each_string];

Example

Let us declare and initialize an array of strings to store the names of 10 computer languages, each with the maximum length of 15 characters.

char langs [10][15]={"PYTHON","JAVASCRIPT","PHP","NODE JS","HTML","KOTLIN","C++","REACT JS","RUST","VBSCRIPT"};

Printing An Array of Strings

A string can be printed using the printf() function with %s format specifier. To print each string of an array of strings, you can use the for loop till the number of strings.

Example

In the following example, we are declaring, initializing, and printing an array of string −

#include <stdio.h>intmain(){char langs [10][15]={"PYTHON","JAVASCRIPT","PHP","NODE JS","HTML","KOTLIN","C++","REACT JS","RUST","VBSCRIPT"};for(int i =0; i <10; i++){printf("%s\n", langs[i]);}return0;}

Output

When you run this code, it will produce the following output −

PYTHON
JAVASCRIPT
PHP
NODE JS
HTML
KOTLIN
C++
REACT JS
RUST
VBSCRIPT

Note: The size of each string is not equal to the row size in the declaration of the array. The “\0” symbol signals the termination of the string and the remaining cells in the row are empty. Thus, a substantial part of the memory allocated to the array is unused and thus wasted.

How an Array of Strings is Stored in Memory?

We know that each char type occupies 1 byte in the memory. Hence, this array will be allocated a block of 150 bytes. Although this block is contagious memory locations, each group of 15 bytes constitutes a row.

Assuming that the array is located at the memory address 1000, the logical layout of this array can be shown as in the following figure −

An Array of Strings with Pointers

To use the memory more efficiently, we can use the pointers. Instead of a 2D char array, we declare a 1D array of “char *” type.

char*langs[10]={"PYTHON","JAVASCRIPT","PHP","NODE JS","HTML","KOTLIN","C++","REACT JS","RUST","VBSCRIPT"};

In the 2D array of characters, the strings occupied 150 bytes. As against this, in an array of pointers, the strings occupy far less number of bytes, as each string is randomly allocated memory as shown below −

Note: Here, lang[ ] is an array of pointers of individual strings.

Example

We can use a for loop as follows to print the array of strings −

#include <stdio.h>intmain(){char*langs[10]={"PYTHON","JAVASCRIPT","PHP","NODE JS","HTML","KOTLIN","C++","REACT JS","RUST","VBSCRIPT"};for(int i =0; i <10; i++)printf("%s\n", langs[i]);return0;}

Output

When you run this code, it will produce the following output −

PYTHON
JAVASCRIPT
PHP
NODE JS
HTML
KOTLIN
C++
REACT JS
RUST
VBSCRIPT

Here, langs is a pointer to an array of 10 strings. Therefore, if langs[0] points to the address 5000, then “langs + 1” will point to the address 5004 which stores the pointer to the second string.

Hence, we can also use the following variation of the loop to print the array of strings −

for(int i =0; i <10; i++){printf("%s\n",*(langs + i));}

When strings are stored in array, there are a lot use cases. Let study some of the use cases.

Find the String with the Largest Length

In the following example, we store the length of first string and its position (which is “0”) in the variables “l” and “p” respectively. Inside the for loop, we update these variables whenever a string of larger length is found.

Example

Take a look at the following example −

#include <stdio.h>#include <string.h>intmain(){char langs [10][15]={"PYTHON","JAVASCRIPT","PHP","NODE JS","HTML","KOTLIN","C++","REACT JS","RUST","VBSCRIPT"};int l =strlen(langs[0]);int p =0;for(int i =0; i <10; i++){if(strlen(langs[i])>= l){
     l =strlen(langs&#91;i]);
     p = i;}}printf("Language with the longest name: %s Length: %d", langs&#91;p], l);return0;}</code></pre>


Output



When you run this code, it will produce the following output −



Language with longest name: JAVASCRIPT Length:10



Sort a String Array in Ascending Order



We need to use the strcmp() function to compare two strings. If the value of comparison of strings is greater than 0, it means the first argument string appears later than the second in alphabetical order. We then swap these two strings using the strcmp() function.



Example



Take a look at the following example −



#include <stdio.h>#include <string.h>intmain(){char langs [10][15]={"PYTHON","JAVASCRIPT","PHP","NODE JS","HTML","KOTLIN","C++","REACT JS","RUST","VBSCRIPT"};int i, j;char temp[15];for(i =0; i <9; i++){for(j = i +1; j <10; j++){if(strcmp(langs[i], langs[j])>0){strcpy(temp, langs[i]);strcpy(langs[i], langs[j]);strcpy(langs[j], temp);}}}for(i =0; i <10; i++){printf("%s\n", langs[i]);}return0;}



Output



When you run this code, it will produce the following output −



C++
HTML
JAVASCRIPT
KOTLIN
NODE JS
PHP
PYTHON
REACT JS
RUST
VBSCRIPT




In this chapter, we explained how you can declare an array of strings and how you can manipulate it with the help of string functions.