Arrays and Strings in C Programming

Array

An array is a collection of multiple values of the same data type stored in contiguous memory locations under a single variable name.

Each element of an array can be accessed using its index number.

In C, array indexing always begins from 0.

For example, if an array has 5 elements, its indexes are:

0, 1, 2, 3, 4

Therefore, an array of size 5 contains exactly five elements.

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Array Declaration

Syntax

data_type array_name[size];

Example

int a[5];

Here:

• int → Data type
• a → Array name
• 5 → Number of elements

The elements are:

a[0]
a[1]
a[2]
a[3]
a[4]

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Features of Array

The important features of an array are:

1. An array can store multiple values under a single variable name.
2. All elements of an array must normally be of the same data type.
3. Array elements are stored in contiguous memory locations.
4. Each element is accessed using an index.
5. Array indexing begins from 0.
6. Arrays make it easier to process a large number of similar values.
7. Array elements can be processed efficiently using loops.

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Types of Array

The main types of arrays are:

1. One-Dimensional Array
2. Two-Dimensional Array

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1. One-Dimensional Array

An array having only one subscript or index is called a one-dimensional array.

It is used to store a list of values of the same data type.

Syntax

data_type array_name[size];

Example

int marks[5];

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Initialization of a One-Dimensional Array

An array can be initialized at the time of declaration.

Example

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

Here:

a[0] = 1
a[1] = 2
a[2] = 3
a[3] = 4
a[4] = 5

Notice that although the size is 5, the last index is 4.

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Another Method

The size may be omitted when values are provided during initialization.

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

The compiler automatically determines that the array contains five elements.

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Example of One-Dimensional Array

#include <stdio.h>

int main(void)
{
    int numbers[5] = {10, 20, 30, 40, 50};
    int i;

    printf("Elements of the array:\n");

    for (i = 0; i < 5; i++)
    {
        printf("%d\n", numbers[i]);
    }

    return 0;
}

Output

Elements of the array:
10
20
30
40
50

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Accessing Array Elements

Array elements are accessed using their indexes.

For example:

int a[5] = {2, 4, 8, 12, 16};

The elements can be accessed as:

a[0] = 2
a[1] = 4
a[2] = 8
a[3] = 12
a[4] = 16

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2. Two-Dimensional Array

An array having two subscripts or indexes is called a two-dimensional array.

A two-dimensional array is commonly used to represent:

• Tables
• Rows and columns
• Matrices

Syntax

data_type array_name[rows][columns];

Example

int matrix[2][3];

This creates a matrix containing:

• 2 rows
• 3 columns
• 6 total elements

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Initialization of Two-Dimensional Array

A two-dimensional array can be initialized as follows:

int matrix[2][3] =
{
    {1, 2, 3},
    {4, 5, 6}
};

It represents:

	Column 0	Column 1	Column 2
Row 0	1	2	3
Row 1	4	5	6

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Example of Two-Dimensional Array

#include <stdio.h>

int main(void)
{
    int matrix[2][3] =
    {
        {1, 2, 3},
        {4, 5, 6}
    };

    int i, j;

    for (i = 0; i < 2; i++)
    {
        for (j = 0; j < 3; j++)
        {
            printf("%d ", matrix[i][j]);
        }

        printf("\n");
    }

    return 0;
}

Output

1 2 3
4 5 6

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String

A string is a sequence of characters stored one after another and terminated by a special null character:

\0

In C, strings are generally stored using character arrays.

The <string.h> header file provides several functions for performing operations on strings.

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Declaration of String

Syntax

char string_name[size];

Example

char name[20];

This creates a character array that can store a string.

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Initialization of String

The initialization of a string is similar to the initialization of a one-dimensional character array.

Consider the word:

computer

It can be initialized in different ways.

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Method 1

char name[] = "computer";

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Method 2

char name[9] =
{
    'c', 'o', 'm', 'p',
    'u', 't', 'e', 'r',
    '\0'
};

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Method 3

char name[9] = "computer";

The extra character is required for the terminating null character \0.

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How a String is Stored

For:

char name[] = "computer";

the characters are stored as:

Index	Character
0	c
1	o
2	m
3	p
4	u
5	t
6	e
7	r
8	\0

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Input and Output of a String

A string can be read using scanf() for simple single-word input.

Example

#include <stdio.h>

int main(void)
{
    char name[20];

    printf("Enter name: ");
    scanf("%19s", name);

    printf("Your name is: %s\n", name);

    return 0;
}

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Array of Strings

An array of strings is used to store several strings under a single array name.

In C, an array of strings can be represented using a two-dimensional character array.

Syntax

char string_name[number_of_strings][size_of_each_string];

Example

char names[3][20];

This can store three strings, with space for up to 19 characters plus the null character in each row.

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Example of Array of Strings

#include <stdio.h>

int main(void)
{
    char names[3][20] =
    {
        "Ram",
        "Sita",
        "Hari"
    };

    int i;

    for (i = 0; i < 3; i++)
    {
        printf("%s\n", names[i]);
    }

    return 0;
}

Output

Ram
Sita
Hari

Arrays of strings can be useful in operations such as:

• Storing names
• Searching strings
• Sorting strings
• Creating lists of words

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String Handling Functions

C provides several predefined functions for manipulating strings.

Most standard string handling functions are declared in:

#include <string.h>

Important string handling functions include:

1. strlen()
2. strcpy()
3. strcat()
4. strcmp()

Some older compilers also provide:

5. strrev()
6. strlwr()
7. strupr()

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1. strlen()

The strlen() function is used to find the length of a string.

It counts the number of characters before the terminating null character \0.

The null character itself is not counted.

Syntax

strlen(string);

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Example of strlen()

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

int main(void)
{
    char s[20];
    int length;

    printf("Enter a string: ");
    scanf("%19s", s);

    length = strlen(s);

    printf("Length of the string is: %d\n", length);

    return 0;
}

Example

If the input is:

Nepal

Output:

Length of the string is: 5

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2. strcpy()

The strcpy() function is used to copy one string into another string.

The contents of the source string are copied to the destination string.

Syntax

strcpy(destination, source);

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Example of strcpy()

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

int main(void)
{
    char a[30];
    char b[30];

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

    strcpy(b, a);

    printf("Value of a: %s\n", a);
    printf("Value of b: %s\n", b);

    return 0;
}

Example Output

Enter a string: Nepal
Value of a: Nepal
Value of b: Nepal

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3. strcat()

The strcat() function is used to join or concatenate two strings.

It appends the source string to the end of the destination string.

The final result is stored in the destination string.

Syntax

strcat(destination, source);

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Example of strcat()

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

int main(void)
{
    char name[50];
    char message[100] = "Hello, ";

    printf("Enter your name: ");
    scanf("%49s", name);

    strcat(message, name);

    printf("Final message: %s\n", message);

    return 0;
}

Example Output

Enter your name: Ram
Final message: Hello, Ram

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4. strcmp()

The strcmp() function is used to compare two strings.

The comparison is performed character by character.

Syntax

strcmp(string1, string2);

The function returns:

• 0 if both strings are equal.
• A value less than 0 if the first string comes before the second.
• A value greater than 0 if the first string comes after the second.

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Example of strcmp()

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

int main(void)
{
    char name[100];
    char storedName[] = "John";
    int result;

    printf("Enter a name: ");
    scanf("%99s", name);

    result = strcmp(name, storedName);

    if (result == 0)
    {
        printf("Entered name matches the stored name.\n");
    }
    else
    {
        printf("Entered name does not match the stored name.\n");
    }

    return 0;
}

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5. strrev()

The strrev() function is used in some compilers to reverse the characters of a string.

Syntax

strrev(string);

Example

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

int main(void)
{
    char string[100];

    printf("Enter a string: ");
    scanf("%99s", string);

    strrev(string);

    printf("Reversed string: %s\n", string);

    return 0;
}

For example:

Input: Nepal
Output: lapeN

Note: strrev() is not part of the ISO standard C library. It is available only in some compilers and environments.

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6. strlwr()

The strlwr() function converts uppercase characters in a string into lowercase characters.

Syntax

strlwr(string);

Example

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

int main(void)
{
    char name[100];

    printf("Enter a name in uppercase: ");
    scanf("%99s", name);

    strlwr(name);

    printf("Lowercase: %s\n", name);

    return 0;
}

Example

Input: NEPAL
Output: nepal

Note: strlwr() is not part of the standard C library and may not be supported by modern compilers.

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7. strupr()

The strupr() function converts lowercase characters in a string into uppercase characters.

Syntax

strupr(string);

Example

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

int main(void)
{
    char name[100];

    printf("Enter a name in lowercase: ");
    scanf("%99s", name);

    strupr(name);

    printf("Uppercase: %s\n", name);

    return 0;
}

Example

Input: nepal
Output: NEPAL

Note: strupr() is also a compiler-specific function and is not part of the ISO standard C library.

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Difference Between strlen(), strcpy(), strcat() and strcmp()

Function	Purpose
strlen()	Finds the length of a string
strcpy()	Copies one string to another
strcat()	Joins two strings
strcmp()	Compares two strings

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Additional String Functions

The <string.h> library also provides several other useful standard functions.

Examples

strncpy()
strncat()
strncmp()
strchr()
strstr()

These functions provide additional ways to copy, join, compare, and search strings.

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Difference Between Array and String

Array	String
An array stores multiple values of the same data type.	A string stores a sequence of characters.
It can be an array of integers, floats, characters, etc.	It is normally represented using a character array.
Elements are accessed using indexes.	Characters are also accessed using indexes.
An ordinary array does not require a null terminator.	A C string ends with the null character \0.
Example: int a[5]	Example: char name[20]

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Quick Revision

Array

An array stores multiple values of the same data type using a single variable name.

Syntax

int a[5];

Array indexing starts from:

0

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One-Dimensional Array

Contains one index.

int a[5];

---

Two-Dimensional Array

Contains two indexes.

int a[2][3];

It is commonly used for matrix and table-related problems.

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String

A string is a sequence of characters terminated by:

\0

Example:

char name[] = "Nepal";

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Array of Strings

A two-dimensional character array can store multiple strings.

char names[5][20];

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Important String Functions

strlen() → Finds string length
strcpy() → Copies a string
strcat() → Joins strings
strcmp() → Compares strings

Compiler-specific functions commonly taught in older C environments include:

strrev() → Reverses a string
strlwr() → Converts to lowercase
strupr() → Converts to uppercase

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Important Exam Points

• An array stores multiple values of the same data type.
• Array elements are stored in contiguous memory locations.
• Array indexing begins from 0.
• An array of size 5 has indexes from 0 to 4.
• A one-dimensional array has one subscript.
• A two-dimensional array has two subscripts.
• Two-dimensional arrays are commonly used to represent matrices.
• A string is a sequence of characters.
• Every valid C string ends with the null character \0.
• Strings are commonly represented using character arrays.
• <string.h> contains declarations for standard string-handling functions.
• strlen() finds the length of a string.
• strcpy() copies one string to another.
• strcat() concatenates strings.
• strcmp() compares strings.
• strrev(), strlwr(), and strupr() are not standard ISO C functions and may only be available in certain compilers.