One-dimensional arrays in C

Introduction

One-dimensional arrays help you store many values of the same type in a single list. This makes it easy to organize and use data like numbers or letters together.

When you want to keep a list of student scores in a test.

When you need to store daily temperatures for a week.

When you want to hold a sequence of characters as a word or sentence.

When you want to process a list of items one by one.

When you want to perform calculations on a fixed number of values.

Syntax

C

/* Define an array of integers with 5 elements */
int numbers[5];

/* Define and initialize an array of characters */
char letters[4] = {'a', 'b', 'c', 'd'};

The number inside the square brackets [] tells how many items the array can hold.

Array indexes start at 0, so the first element is numbers[0].

Examples

This creates an array of 3 integers but does not set their values yet.

C

int scores[3];

// Empty array of 3 integers, values are garbage until assigned

Here, the array is created and filled with 5 prime numbers right away.

C

int primes[5] = {2, 3, 5, 7, 11};

// Array with 5 prime numbers initialized

This array holds the word "Hello" as characters, ending with '\0' to mark the end.

C

char word[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

// Array holding a string with null terminator

Some compilers allow zero-length arrays as an extension, but they cannot hold any elements.

C

int emptyArray[0];

// Edge case: array with zero length (not standard in C, but allowed as a compiler extension in some compilers)

Sample Program

This program creates an array to hold temperatures for 5 days. It prints all the temperatures, changes the temperature for day 3, and prints the updated list.

C

#include <stdio.h>

int main() {
    // Create an array of 5 integers
    int temperatures[5] = {23, 25, 22, 20, 24};

    // Print all temperatures
    printf("Temperatures for the week:\n");
    for (int index = 0; index < 5; index++) {
        printf("Day %d: %d degrees\n", index + 1, temperatures[index]);
    }

    // Change the temperature of day 3
    temperatures[2] = 26;

    // Print updated temperatures
    printf("\nUpdated temperatures:\n");
    for (int index = 0; index < 5; index++) {
        printf("Day %d: %d degrees\n", index + 1, temperatures[index]);
    }

    return 0;
}

Important Notes

Accessing an array index outside its range causes undefined behavior and can crash your program.

Arrays have fixed size; you cannot change their length after creation.

Time complexity to access any element by index is O(1), which means very fast.

Summary

One-dimensional arrays store multiple values of the same type in order.

Use arrays when you need to keep and work with lists of data.

Remember array indexes start at 0 and size is fixed.