Strings in C

String in C programming is a sequence of characters terminated with a null character ‘\0’. Strings are defined as an array of characters. The difference between a character array and a string is the string is terminated with a unique character ‘\0’.

Example of C String:

Declaration of Strings

Declaring a string is as simple as declaring a one-dimensional array. Below is the basic syntax for declaring a string.

char str_name[size];

In the above syntax str_name is any name given to the string variable and size is used to define the length of the string, i.e the number of characters strings will store. 
Note: There is an extra terminating character which is the Null character (‘\0’) used to indicate the termination of a string that differs strings from normal character arrays. When a Sequence of characters enclosed in the double quotation marks is encountered by the compiler, a null character ‘\0’ is appended at the end of the string by default.

Initializing a String

A string can be initialized in different ways. We will explain this with the help of an example. Below are the examples to declare a string with the name str and initialize it with “GeeksforGeeks”.

4 Ways to Initialize a String in C

1. Assigning a string literal without size: String literals can be assigned without size. Here, the name of the string str acts as a pointer because it is an array.

char str[] = "GeeksforGeeks"; 

2. Assigning a string literal with a predefined size: String literals can be assigned with a predefined size. But we should always account for one extra space which will be assigned to the null character. If we want to store a string of size n then we should always declare a string with a size equal to or greater than n+1.

char str[50] = "GeeksforGeeks";

3. Assigning character by character with size: We can also assign a string character by character. But we should remember to set the end character as ‘\0’ which is a null character.

char str[14] = { 'G','e','e','k','s','f','o','r','G','e','e','k','s','\0'};

4. Assigning character by character without size: We can assign character by character without size with the NULL character at the end. The size of the string is determined by the compiler automatically.

char str[] = { 'G','e','e','k','s','f','o','r','G','e','e','k','s','\0'};

Below is the memory representation of the string “Geeks”. 

Let us now look at a sample program to get a clear understanding of declaring, initializing a string in C, and also how to print a string with its size. 

C

// C program to illustrate strings

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

int main()
{
    // declare and initialize string
    char str[] = "Geeks";

    // print string
    printf("%s\n", str);

    int length = 0;
    length = strlen(str);

    // displaying the length of string
    printf("Length of string str is %d", length);

    return 0;
}

Output

Geeks
Length of string str is 5

We can see in the above program that strings can be printed using normal printf statements just like we print any other variable. Unlike arrays, we do not need to print a string, character by character. 
Note: The C language does not provide an inbuilt data type for strings but it has an access specifier “%s” which can be used to print and read strings directly. 

How to Read a String From User?

C

// C program to read string from user
#include<stdio.h>

int main()
{
    // declaring string
    char str[50];

    // reading string
    scanf("%s",str);

    // print string
    printf("%s",str);

    return 0;
}

Input:
GeeksforGeeks

Output:
GeeksforGeeks

You can see in the above program that the string can also be read using a single scanf statement. Also, you might be thinking that why we have not used the ‘&’ sign with the string name ‘str’ in scanf statement! To understand this you will have to recall your knowledge of scanf. 
We know that the ‘&’ sign is used to provide the address of the variable to the scanf() function to store the value read in memory. As str[] is a character array so using str without braces ‘[‘ and ‘]’ will give the base address of this string. That’s why we have not used ‘&’ in this case as we are already providing the base address of the string to scanf.

How to Read a Line of Text in C?

We can use the fgets() function to read a line of string and gets() to read characters from the standard input  (stdin) and store them as a C string until a newline character or the End-of-file (EOF) is reached.

For Example:

C

// C program to illustrate
// fgets()
#include <stdio.h>
#define MAX 50
int main()
{
    char str[MAX];

    // MAX Size if 50 defined
    fgets(str, MAX, stdin);

    printf("String is: \n");

    // Displaying Strings using Puts
    puts(str);

    return 0;
}

Input:
GeeksforGeeks

Output:
String is:
GeeksforGeeks

Passing Strings to Function

As strings are character arrays, so we can pass strings to function in the same way we pass an array to a function. Below is a sample program to do this: 

C

// C program to illustrate how to
// pass string to functions
#include <stdio.h>

void printStr(char str[]) { printf("String is : %s", str); }

int main()
{
    // declare and initialize string
    char str[] = "GeeksforGeeks";

    // print string by passing string
    // to a different function
    printStr(str);

    return 0;
}

Output:

String is : GeeksforGeeks

Note: We can’t read a string value with spaces, we can use either gets() or fgets() in the C programming language.

Strings and Pointers

In Arrays, the variable name points to the address of the first element. Similar to Arrays in C we can create a character pointer to a string that points to the starting address of the string which is the first character of the string. The string can be accessed with the help of pointers as shown in the below example. 

C

// C program to print string using Pointers
#include <stdio.h>

int main()
{

    char str[20] = "GeeksforGeeks";

    // Pointer variable which stores
    // the starting address of
    // the character array str
    char* ptr = str;

    // While loop will run till
    // the character value is not
    // equal to null character
    while (*ptr != '\0') {
        printf("%c", *ptr);

        // moving pointer to the next character.
        ptr++;
    }

    return 0;
}

Output

GeeksforGeeks

Most Used Functions in C  Strings:

Function Name	Description
strlen(string_name)	Returns the length of string name.
strcpy(s1, s2)	Copies the contents of string s2 to string s1.
strcmp(str1, str2)	Compares the first string with the second string. If strings are the same it returns 0.
strcat(s1, s2)	Concat s1 string with s2 string and the result is stored in the first string.
strlwr()	Converts string to lowercase.
strupr()	Converts string to uppercase.
strstr(s1, s2)	Find the first occurrence of s2 in s1.

This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please write comments if you find anything incorrect, or if you want to share more information about the topic discussed above.