Arrays in C

# CHAPTER 10

Arrays in C #

1. Introduction #

2. Learning Objectives #

• Declare and initialize arrays.

• Access array elements using indices.

• Traverse arrays using loops.

• Understand how arrays are stored in memory.

• Perform basic searching in an array.

3. Declaring and Initializing Arrays #

int grades[5]; // Declares an array of 5 integers

Initialization:

// Method 1: Initializing at declaration
int scores[5] = {85, 90, 78, 92, 88};

// Method 2: Size is inferred from the elements
int ages[] = {20, 22, 21, 25}; 

// Method 3: Partial initialization (rest become 0)
int zeros[5] = {10, 20}; // {10, 20, 0, 0, 0}

4. Accessing Array Elements #

int scores[5] = {85, 90, 78, 92, 88};

printf("First score: %d\n", scores[0]); // 85
printf("Third score: %d\n", scores[2]); // 78

// Modifying an element
scores[1] = 95; // Changes the second element from 90 to 95

5. Traversing an Array with Loops #

int scores[5] = {85, 95, 78, 92, 88};

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

6. Passing Arrays to Functions #

#include <stdio.h>

void printArray(int arr[], int size) {
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    int numbers[] = {1, 2, 3, 4, 5};
    printArray(numbers, 5);
    return 0;
}

7. Mini Project: Marks Management System #

#include <stdio.h>

int main() {
    int marks[5];
    int sum = 0;
    float average;

    printf("=== MARKS MANAGEMENT ===\n");
    // Get input
    for (int i = 0; i < 5; i++) {
        printf("Enter marks for subject %d: ", i + 1);
        scanf("%d", &marks[i]);
    }

    // Calculate sum
    for (int i = 0; i < 5; i++) {
        sum += marks[i];
    }

    average = (float)sum / 5; // Type casting for decimal accuracy

    printf("Total Marks: %d\n", sum);
    printf("Average: %.2f\n", average);

    return 0;
}

8. Memory-Level Explanation #

int arr[3] = {10, 20, 30};

Memory Layout:
+----------------+
| arr[0] = 10    | <- Address 2000
+----------------+
| arr[1] = 20    | <- Address 2004
+----------------+
| arr[2] = 30    | <- Address 2008
+----------------+

Because the memory is contiguous, the CPU can access elements instantly using math: Address = Base_Address + (Index * Data_Size).

9. Common Mistakes #

• Out of Bounds Access: In C, there is no boundary checking. If you declare int arr[5], and try to access arr[10], C will blindly read whatever is in that memory location, causing garbage values or a Segmentation Fault (crash).

• Index starts at 1: Forgetting that arrays start at 0. The last element of arr[5] is arr[4].

10. Exercises #

1. 1. Write a program to find the maximum number in an array.

1. 2. Write a program that reverses the elements of an array.

1. 3. Write a program to search for a specific number in an array (Linear Search) and print its index.

11. MCQ Quiz with Answers #

12. Interview Questions #

• Q: Why do arrays in C start at index 0?

• Q: How is an array passed to a function (pass by value or reference)? Explain why.

• Q: What is the formula to calculate the memory address of the i-th element of a 1D array?

13. Summary #

14. Next Chapter Recommendation #