Arrays · C · CodeMIRAI

Arrays

2 min read 4 runnable examples Quiz included

An array holds a fixed number of values of the same type, side by side in memory.

An array is one block of memory. Indexing is arithmetic on the start address, which is why a[5] runs off the end silently.

#include <stdio.h>

int main() {
    int scores[5] = {72, 95, 88, 61, 79};

    printf("First: %d\n", scores[0]);
    printf("Last: %d\n", scores[4]);

    scores[3] = 65;     // change an element
    for (int i = 0; i < 5; i++) {
        printf("scores[%d] = %d\n", i, scores[i]);
    }
    return 0;
}

Indexes start at 0, so an array of 5 has indexes 0 to 4.

Total, average and maximum

#include <stdio.h>

int main() {
    int values[6] = {4, 8, 15, 16, 23, 42};
    int n = 6, total = 0, max = values[0];

    for (int i = 0; i < n; i++) {
        total += values[i];
        if (values[i] > max) max = values[i];
    }
    printf("Total %d, average %.2f, max %d\n", total, (double)total / n, max);
    return 0;
}

Passing arrays to functions

A function can't tell how long an array is, so pass the length too:

#include <stdio.h>

int sum(int arr[], int length) {
    int s = 0;
    for (int i = 0; i < length; i++) s += arr[i];
    return s;
}

int main() {
    int a[4] = {1, 2, 3, 4};
    int b[3] = {10, 20, 30};
    printf("%d %d\n", sum(a, 4), sum(b, 3));
    return 0;
}

Unlike ordinary variables, an array passed to a function is not copied: the function works on the original.

Two-dimensional arrays

#include <stdio.h>

int main() {
    int grid[3][3] = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };
    for (int r = 0; r < 3; r++) {
        for (int c = 0; c < 3; c++) {
            printf("%3d", grid[r][c]);
        }
        printf("\n");
    }
    printf("Centre: %d\n", grid[1][1]);
    return 0;
}

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