C Arrays. Storing Multiple Values Under One Variable.

Array is a data type that holds more than one value. It allows you to store multiple values under a single variable name.

In C, arrays are structured like this:

// array_format
type_data array_name[array_size];

Implementing an Array

We are going to implement an array by creating a Date of Birth (DOB) app.

Here's how we do it:

#include <stdio.h>

int date[3];

int main(void)
{
    // Input and validate day
    do {
        printf("Enter day (1-31): ");
        scanf("%d", &date[0]);
        if (date[0] < 1 || date[0] > 31) {
            printf("Invalid day! /n");
        }
    } while (date[0] < 1 || date[0] > 31);

    // Input and validate month
    do {
        printf("Enter month (1-12): ");
        scanf("%d", &date[1]);
        if (date[1] < 1 || date[1] > 12) {
            printf("Invalid month! \n");
        }
    } while (date[1] < 1 || date[1] > 12);

    // Input and validate year (4 digits)
    do {
        printf("Enter year (1000-9999): ");
        scanf("%d", &date[2]);
        if (date[2] < 1000 || date[2] > 9999) {
            printf("Invalid year! Please enter a 4-digit year (between 1000 and 9999).\n");
        }
    } while (date[2] < 1000 || date[2] > 9999);

    // Print the validated date of birth
    printf("Your date of birth is: %02d/%02d/%d\n", date[0], date[1], date[2]);


}

Relationship Between Strings and Arrays

Let's initialize a string:

char *greeting = "hello-world";

The actual underlying representation looks like this:

['h', 'e', 'l', 'l', 'o', '-', 'w', 'o', 'r', 'l', 'd', '\n']

So, in C, a string is essentially an array of characters.

Let's take a look at a complete example where we can access each character in the string by its index:

#include <stdio.h>

int main(void)
{
    char *greeting = "hello-world";
    // The actual output would be: ['h', 'e', 'l', 'l', 'o', '-', 'w', 'o', 'r', 'l', 'd', '\n'];

    printf("%c\n", greeting[1]);  // Output: 'e'
    printf("%c\n", greeting[2]);  // Output: 'l'
    printf("%c\n", greeting[3]);  // Output: 'l'


}

In this example, the program prints the characters at the 1st, 2nd, and 3rd positions of the string "hello-world."