22. C - Strings

In C programming, a string is a sequence of characters terminated with a null character \0. For example:

char c[] = "c string";

When the compiler encounters a sequence of characters enclosed in the double quotation marks, it appends a null character \0 at the end by default.

Strings are actually a one-dimensional array of characters terminated by a null character ‘\0’. Thus a null-terminated string contains the characters that comprise the string followed by a null.

Declare a String

Here’s how you can declare strings:

char s[5];

Here, we have declared a string of 5 characters.

Initialization of Strings

You can initialize strings in a number of ways.

char c[] = "abcd";

char c[50] = "abcd";

char c[] = {'a', 'b', 'c', 'd', '\0'};

char c[5] = {'a', 'b', 'c', 'd', '\0'};

Initialization of strings in C programming

Let’s take another example:

char c[5] = "abcde";

Here, we are trying to assign 6 characters (the last character is '\0') to a char an array having 5 characters. This is bad and you should never do this.

Assigning Values to Strings

Arrays and strings are second-class citizens in C; they do not support the assignment operator once it is declared. For example,

char c[100];
c = "C programming";  // Error! array type is not assignable.

Note: Use the strcpy() function to copy the string instead.

Read String from the user

You can use the scanf() function to read a string.

The scanf() function reads the sequence of characters until it encounters whitespace (space, newline, tab, etc.).

Example 1: scanf() to read a string

#include <stdio.h>
int main()
{
    char name[20];
    printf("Enter name: ");
    scanf("%s", name);
    printf("Your name is %s.", name);
    return 0;
}

Output

Enter name: Dennis Ritchie
Your name is Dennis.

Even though Dennis Ritchie was entered in the above program, only “Dennis” was stored in the name string. It’s because there was a space after Dennis.

Read a line of Text

You can use the fgets() function to read a line of string. And, you can use puts() to display the string.

Example 2: fgets() and puts()

#include <stdio.h>
int main()
{
    char name[30];
    printf("Enter name: ");
    fgets(name, sizeof(name), stdin);  // read string
    printf("Name: ");
    puts(name);    // display string
    return 0;
}

Output

Enter name: Tom Hanks
Name: Tom Hanks

Here, we have used fgets() function to read a string from the user.

fgets(name, sizeof(name), stdlin); // read string

The sizeof(name) results to 30. Hence, we can take a maximum of 30 characters as input which is the size of the name string.

To print the string, we have used puts(name);.

Note: The gets() function can also be to take input from the user. However, it is removed from the C standard.

It’s because gets() allows you to input any length of characters. Hence, there might be a buffer overflow.

Passing Strings to Functions

Strings can be passed to a function in a similar way as arrays. Learn more about passing arrays to a function.

Example 3: Passing string to a Function

#include <stdio.h>
void displayString(char str[]);

int main()
{
    char str[50];
    printf("Enter string: ");
    fgets(str, sizeof(str), stdin);             
    displayString(str);     // Passing string to a function.    
    return 0;
}
void displayString(char str[])
{
    printf("String Output: ");
    puts(str);
}

String Library Functions form <string.h>

C supports a wide range of functions that manipulate null-terminated strings −

Sr.No.	Function & Purpose
1	strcpy(s1, s2);Copies string s2 into string s1.
2	strcat(s1, s2);Concatenates string s2 onto the end of string s1.
3	strlen(s1);Returns the length of string s1.
4	strcmp(s1, s2);Returns 0 if s1 and s2 are the same; less than 0 if s1<s2; greater than 0 if s1>s2.
5	strchr(s1, ch);Returns a pointer to the first occurrence of character ch in string s1.
6	strstr(s1, s2);Returns a pointer to the first occurrence of string s2 in string s1.

22. C – Strings