Lesson 5: Arrays

An array is a fixed-size, sequenced collection of elements all of the same data type, stored in contiguous memory locations and accessed through a single name plus an index.

Key characteristics:

• All elements are the same type.
• Elements are indexed starting from 0.
• The index can be a variable, allowing loops to process every element efficiently.
• The array name refers to the address of the first element in memory.

Element address formula:

element address = array address + (sizeof(element) × index)

The formula, worked on a real array:

Declaration Syntax

data_type array_name[size];

int scores[20];      // 20-element integer array
char name[30];       // 30-element character array
float averages[10];  // 10-element float array

Initializing at Declaration

int first_array[5] = {5, 3, 2, 7, 9};
int second_array[] = {11, 21, 75, 24, 5};  // size inferred
int third_array[15] = {3, 7, 4, 6, 1};     // remaining 10 → 0

Character Arrays (Strings)

A string in C is a character array terminated by '\0' (null character). The null terminator is added automatically from string literals.

char college[6] = "CCMIT";
// college[0]='C', college[1]='C', ..., college[5]='\0'

Accessing Elements

scores[0]     // first element
scores[9]     // tenth element (for a 10-element array)
scores[i]     // element at variable index i

Reading into an array:

for (i = 0; i < 10; i++)
    scanf("%d", &scores[i]);

Printing:

for (i = 0; i < 10; i++)
    printf("%d\n", scores[i]);

Copying (element by element — arrays cannot be assigned directly):

for (i = 0; i < 25; i++)
    second[i] = first[i];

Bubble Sort — Ascending Order

#include <stdio.h>
#include <conio.h>

void main() {
    clrscr();
    int num[3] = {5, 3, 7};
    int h, i, temp;

    for (h = 0; h < 3; h++)
        for (i = 0; i < h; i++)
            if (num[i] > num[i + 1]) {
                temp = num[i];
                num[i] = num[i + 1];
                num[i + 1] = temp;
            }

    for (i = 0; i < 3; i++)
        printf("%d\n", num[i]);
    getch();
}

Output: 3, 5, 7

Count Positive and Negative Values

void main() {
    int a[50], n, count_neg = 0, count_pos = 0, i;
    printf("Enter the size of the array: ");
    scanf("%d", &n);
    for (i = 0; i < n; i++) scanf("%d", &a[i]);

    for (i = 0; i < n; i++) {
        if (a[i] < 0) count_neg++;
        else count_pos++;
    }

    printf("Negative numbers: %d\n", count_neg);
    printf("Positive numbers: %d\n", count_pos);
}

• An array is a fixed-size group of values of the same type, stored side by side in memory under one name.
• Indexes start at 0, so an array of size n runs from a[0] to a[n-1]. Using a[n] goes past the end.
• Element address = array address + (size of one element × index). That is how C finds any element directly.
• In an initializer, missing values become 0, and int b[] = {11, 21, 75}; lets the compiler count the size for you.
• A string is a char array that ends in '\0', so char college[6] holds the 5 letters of "CCMIT" plus the terminator. Read, print, and copy arrays with a loop: one array cannot be assigned to another with =.

Add more scores to the array (update the size too) and watch the average and max update.