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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’.
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.
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 “Learn C”.
4 Ways to Initialize a String in C
- 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[] = "Learn C"; - 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 '\0'. 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] = "Learn C";- 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[8] = { 'L', 'e', 'a', 'r', 'n', ' ', 'C','\0'};- 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[] = { 'L', 'e', 'a', 'r', 'n', ' ', 'C','\0'};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 program to illustrate strings
#include <stdio.h>
int main()
{
// declare and initialize string
char str[] = "Rishi";
// print string
printf("%s\n", str);
return (0);
}Output:
Rishi
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.
As we have seen, Strings are just arrays of characters, with a null character indicating the end of the string. A string can be accessed and modified just like a normal array.
We can access characters of a string using the index number. For Example:
#include<stdio.h>
int main(void)
{
char greet[] = "Hello World";
printf("%c\n", greet[0]);
return (0);
}Output:
H
Note: We use the character specifier '%c'when printing a single character
We can modify characters of a string, just like we can change values of elements in an array
Example:
#include<stdio.h>
int main(void)
{
char greet[] = "Hello World";
greet[1] = 'a'; /* Change the second character from e to a*/
printf("%s\n", greet); /*Hallo World*/
return (0);
}Output:
Hallo World
Strings can contain Special characters as seen above.
C also has many useful string functions, which can be used to perform certain operations on strings.
To use them, you must include the <string.h> header file in your program:
#include <string.h>| 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) | Concatenate 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. |
We would look at some of the above Functions in the next Chapter: More Strings
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