Arrays (1-D)

Notes

Arrays (1-D)

Definition: An array is a collection of elements of the same data type stored in contiguous memory locations. Each element is identified using an index.

Why Do We Need an Array?

Suppose we need to store the marks of five students. Without an array, we would need five separate variables.

int mark1 = 78;
int mark2 = 65;
int mark3 = 91;
int mark4 = 54;
int mark5 = 82;

An array allows us to store all these values using one variable name.

What is a One-Dimensional Array?

Definition: A one-dimensional array is a linear collection of elements arranged in a single sequence. Each element is accessed using one index.

Characteristics of an Array

• All elements have the same data type.
• Elements are stored in a continuous sequence of memory locations.
• Each element is accessed using an index.
• Array indexing in C starts from 0.
• The size of a normally declared fixed-size array is determined at declaration.

Array Declaration

Definition: Array declaration tells the compiler the data type, name and number of elements of the array.

data_type array_name[size];

Array Initialization

Definition: Array initialization means assigning initial values to the array elements.

int marks[5] = {78, 65, 91, 54, 82};

Declaration vs Initialization

Array Size

Definition: The size of an array is the total number of elements it can store.

Remember that array size and last index are different. For an array of size 5, the last valid index is 4.

Indexing in an Array

Definition: Indexing is the method of identifying and accessing individual elements of an array using their position. In C, array indexing starts from 0.

Array with Indexes

Array:    marks

Index:      0    1    2    3    4
            ↓    ↓    ↓    ↓    ↓

Value:     78   65   91   54   82

First and Last Index

Definition: In a one-dimensional array, the first element is always at index 0 and the last element is at index size - 1.

Accessing Array Elements

Definition: An individual array element is accessed by writing the array name followed by its index inside square brackets.

marks[0]
marks[1]
marks[2]

Modifying an Array Element

Definition: An array element can be changed by assigning a new value to its index.

marks[2] = 95;

Traversing an Array

Definition: Traversing an array means visiting each element of the array one by one.

for (int i = 0; i < 5; i++)
{
    printf("%d ", marks[i]);
}

Taking Array Input

Definition: Array elements can be read from the user one by one using a loop and scanf().

Displaying Array Elements

Definition: Array elements can be displayed by accessing each index, usually with the help of a loop.

Array and Memory

Definition: Array elements are stored in consecutive memory locations, which makes sequential access efficient.

Array Initialization with Fewer Values

Definition: An array can be initialized with fewer values than its declared size. The remaining elements are initialized to zero when the array has static initialization in a declaration such as this.

int marks[5] = {78, 65};

Initializing All Elements with Zero

A simple way to initialize all elements of an array to zero is to provide the first element as zero and let the remaining elements be initialized to zero.

int marks[5] = {0};

Array and Loop

Arrays and loops are commonly used together because a loop can process every element using its index.

Practical Example — Read and Display Array Elements

Problem Statement

Write a C program to accept 5 integers from the user and display all the elements of the one-dimensional array.

Learning Outcomes

• Declare and initialize a one-dimensional array.
• Use a loop to accept array elements.
• Use indexes to access and display array elements.

Hint

Use an integer array of size 5. Use one for loop to read the elements and another loop to display them.

Theory

Array elements are accessed using indexes starting from 0. A loop provides a convenient way to process each element in sequence.

Program

#include <stdio.h>

int main()
{
    int marks[5];
    int i;

    printf("Enter 5 integers: ");

    // read each array element
    for (i = 0; i < 5; i++)
        scanf("%d", &marks[i]);

    printf("Array elements: ");

    // display each array element
    for (i = 0; i < 5; i++)
        printf("%d ", marks[i]);

    return 0;
}

Expected Output

Enter 5 integers: 78 65 91 54 82
Array elements: 78 65 91 54 82

Note

Remember that for an array of size 5, the indexes are only 0 through 4. Accessing marks[5] is outside the valid range.

Array Index Out of Bounds

Definition: An out-of-bounds access occurs when a program tries to access an index outside the valid range of the array.

Common Mistakes in Arrays

Finding Sum of Array Elements

Definition: The sum of an array is obtained by adding all its elements together.

int sum = 0;

for (int i = 0; i < 3; i++)
    sum += arr[i];

Finding Average of Array Elements

Definition: The average of array elements is the sum of all elements divided by the number of elements.

Finding Largest Element

Definition: The largest element is the element having the greatest value among all array elements.

Finding Smallest Element

Definition: The smallest element is the element having the lowest value among all array elements.

Searching an Element

Definition: Searching an array means checking its elements to determine whether a particular value is present.

Practical Example — Find Sum and Average

Problem Statement

Write a C program to accept 5 numbers in a one-dimensional array and calculate their sum and average.

Learning Outcomes

• Store multiple values in a one-dimensional array.
• Traverse an array using a loop.
• Calculate sum and average from array elements.

Hint

Initialize sum to 0. Add every array element to sum, then divide the sum by 5.0.

Theory

The sum of array elements can be calculated by traversing the array and adding each element to a running total. The average is obtained by dividing the total by the number of elements.

Program

#include <stdio.h>

int main()
{
    int arr[5];
    int i, sum = 0;
    float average;

    printf("Enter 5 numbers: ");

    // read array elements
    for (i = 0; i < 5; i++)
        scanf("%d", &arr[i]);

    // calculate the sum
    for (i = 0; i < 5; i++)
        sum += arr[i];

    average = sum / 5.0;     // use 5.0 for floating-point division

    printf("Sum = %d
", sum);
    printf("Average = %.2f
", average);

    return 0;
}

Expected Output

Enter 5 numbers: 10 20 30 40 50
Sum = 150
Average = 30.00

Note

When a fractional average is required, use a floating-point divisor such as 5.0 instead of 5 to avoid unintended integer division.

Quick Revision

Important Exam Questions

Short Answer Questions

1. What is an array?
2. What is a one-dimensional array?
3. Why are arrays used in C?
4. Write the syntax for declaring an array.
5. What is array indexing?
6. Why does array indexing start from 0 in C?
7. What is the last valid index of an array of size 10?
8. What is array traversal?
9. What is an out-of-bounds array access?
10. How are array elements accessed?

Long Answer Questions

1. Define an array and explain one-dimensional arrays with examples.
2. Explain array declaration, initialization and indexing in C.
3. Explain how to access, modify and traverse a one-dimensional array.
4. Write a C program to read and display elements of a one-dimensional array.
5. Write a C program to find the sum and average of array elements.
6. Explain common mistakes while working with one-dimensional arrays.