Input an Array in C

Arrays in C store contiguous elements of identical type in physical RAM. Learn array declarations, O(1) index math, multi-dimensional layouts, and boundary protection.

Arrays are the most fundamental contiguous data structure in C. They group elements of identical type together in adjacent physical memory addresses, granting O(1) constant-time access via direct index offset math.

C uses zero-based indexing: an array int arr[5] has valid indices from 0 to 4. When an array name appears in most expressions, it automatically decays into a pointer to its first element (&arr[0]).

Because C prioritizes raw execution speed over defensive checks, the compiler never performs runtime array boundary validation. Reading or writing past an array boundary is a major cause of segmentation faults and security vulnerabilities.

Interactive Runnable C Implementation

#include <stdio.h>

#define MAX_SIZE 100

int main(void) {
    int arr[MAX_SIZE];
    int n;
    int sum = 0;

    printf("Enter number of elements (1 to %d): \n", MAX_SIZE);
    if (scanf("%d", &n) != 1 || n <= 0 || n > MAX_SIZE) {
        fprintf(stderr, "Error: Invalid number of elements.\n");
        return 1;
    }

    printf("Reading %d integers from input...\n", n);
    for (int i = 0; i < n; i++) {
        if (scanf("%d", &arr[i]) != 1) {
            fprintf(stderr, "Error reading element at index %d.\n", i);
            return 1;
        }
        sum += arr[i];
    }

    printf("\n--- Array Elements Summary ---\n");
    for (int i = 0; i < n; i++) {
        printf("arr[%d] = %d (Address: %p)\n", i, arr[i], (void *)&arr[i]);
    }

    double average = (double)sum / n;
    printf("\nTotal Sum = %d\n", sum);
    printf("Average   = %.2f\n", average);

    return 0;
}

Open example in compiler

Expected Output

Enter number of elements (1 to 100): 
Reading 5 integers from input...

--- Array Elements Summary ---
arr[0] = 10 (Address: 0x...)
arr[1] = 25 (Address: 0x...)
arr[2] = 40 (Address: 0x...)
arr[3] = 55 (Address: 0x...)
arr[4] = 70 (Address: 0x...)

Total Sum = 200
Average   = 40.00