Character arrays and Strings

Notes

Character Arrays and Strings

Definition: A character array is an array whose elements are of type char. It can store individual characters and can also be used to store a string.

What is a String?

Definition: A string in C is a sequence of characters terminated by a special character called the null character \0.

Character Array vs String

Null Character (\0)

Definition: The null character \0 marks the end of a string in C. It is automatically added when a string literal is used to initialize a character array with enough space.

Declaring a Character Array

Definition: A character array is declared using the char data type followed by the array name and size.

char name[20];

Initializing a String

A string can be initialized using a string literal enclosed in double quotation marks.

char name[] = "Amit";

String Indexing

Definition: Each character in a string is accessed using its index. Like other C arrays, string indexing starts from 0.

String:   H   E   L   L   O   \0
Index:    0   1   2   3   4    5

Accessing a Character

An individual character of a string can be accessed by using the string name and its index.

Modifying a Character

An individual character in a character array can be changed by assigning a new character to its index.

String Traversal

Definition: String traversal means visiting each character one by one until the null character \0 is reached.

for (int i = 0; name[i] != '\0'; i++)
{
    printf("%c ", name[i]);
}

Input of a String

A string can be read from the user using functions such as scanf() or fgets(). For a simple space-free word, scanf("%s", name) can be used.

Output of a String

A string can be displayed using printf() with the %s format specifier.

String Length

Definition: String length is the number of characters present in the string, excluding the terminating null character \0.

String Library Functions

C provides commonly used string functions through the string.h header file.

Practical Example — Read and Display a String

Problem Statement

Write a C program to accept a student's name and display the name using a character array.

Learning Outcomes

• Declare and use a character array.
• Accept a string from the user.
• Display a string using printf().

Hint

Declare a character array and use scanf("%s", name) to read a simple name without spaces.

Theory

A C string is stored in a character array and ends with the null character \0. The %s format specifier is used with printf() to display a string.

Program

#include <stdio.h>

int main()
{
    char name[30];

    printf("Enter your name: ");
    scanf("%29s", name);

    // display the entered string
    printf("Name = %s
", name);

    return 0;
}

Expected Output

Enter your name: Rahul
Name = Rahul

Note

scanf("%s", name) reads a word until whitespace. For input containing spaces, functions such as fgets() are more suitable.

Practical Example — Find String Length

Problem Statement

Write a C program to accept a string and find its length using strlen().

Learning Outcomes

• Use the string.h header file.
• Use the strlen() function.
• Understand that the null character is not counted in string length.

Hint

Include string.h and pass the string to strlen().

Theory

The strlen() function returns the number of characters in a string before the terminating null character.

Program

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

int main()
{
    char name[30];
    int length;

    printf("Enter a word: ");
    scanf("%29s", name);

    length = strlen(name);       // find the number of characters

    printf("Length = %d
", length);

    return 0;
}

Expected Output

Enter a word: COMPUTER
Length = 8

Note

strlen() counts the characters in the string but does not count the terminating \0.

Common Mistakes

Important Points for Exam

• A character array stores elements of type char.
• A C string is a character sequence terminated by \0.
• String indexing starts from 0.
• %s is commonly used to read or display strings.
• strlen() returns the string length excluding \0.
• The string.h header provides common string functions.

Quick Revision

Important Exam Questions

Short Answer Questions

1. What is a character array?
2. What is a string in C?
3. What is the null character \0?
4. Why does a string require an extra position for \0?
5. How are characters of a string accessed?
6. What is the use of strlen()?
7. What is the purpose of string.h?
8. Differentiate between a character array and a string.

Long Answer Questions

1. Define character arrays and strings. Explain their declaration, initialization and indexing with examples.
2. Explain the role of the null character in C strings.
3. Explain common string functions such as strlen(), strcpy(), strcat() and strcmp().
4. Write a C program to read and display a string.
5. Write a C program to find the length of a string.