Foundations Updated 2026-09 View as Markdown

Arrays

Arrays are special variables which can hold more than one value under the same variable name, organised with an index.

Arrays are special variables which can hold more than one value under the same variable name, organised with an index. Arrays are defined using a very straightforward syntax:

/* defines an array of 10 integers */
int numbers[10];

Accessing a number from the array is done using the same syntax. Notice that arrays in C are zero-based, which means that if we defined an array of size 10, then the array cells 0 through 9 (inclusive) are defined. numbers[10] is not an actual value.

int numbers[10];

/* populate the array */
numbers[0] = 10;
numbers[1] = 20;
numbers[2] = 30;
numbers[3] = 40;
numbers[4] = 50;
numbers[5] = 60;
numbers[6] = 70;

/* print the 7th number from the array, which has an index of 6 */
printf("The 7th number in the array is %d", numbers[6]);

Arrays can only have one type of variable, because they are implemented as a sequence of values in the computer’s memory. Because of that, accessing a specific array cell is very efficient.

The average of the 3 grades is: 85

#include <stdio.h>

int main() {
    /* TODO: define the grades variable here */
    int grades[3];
    int average;

    grades[0] = 80;
    /* TODO: define the missing grade
        so that the average will sum to 85. */
    grades[1] = 85;
    grades[2] = 90;

    average = (grades[0] + grades[1] + grades[2]) / 3;
    printf("The average of the 3 grades is: %d", average);

    return 0;
}