Example of OOP in C.

oop.c

#include <stdlib.h>
#include <stdio.h>

typedef struct Array {
    int* arr;
    size_t length;
} Array;

Array* newArray(int len)
{
    Array* ptr = malloc(sizeof(Array));
    ptr->arr = malloc(sizeof(int) * len);
    ptr->length = len;
    return ptr;
}

void deleteArray(Array* obj) 
{
    free(obj->arr);
    free(obj);
}

void assign(Array* obj, size_t index, int x)
{
    if (index > obj->length)
        return;
    else
        obj->arr[index] = x;
}

int getNum(Array* obj, size_t index)
{
    if (index > obj->length)
        return 0;
    else
        return obj->arr[index];
}

int main()
{
    size_t i;
    Array* arr = newArray(10);
    for (i = 0; i < arr->length; i++) {
        assign(arr, i, i * 100);
    }
    for (i = 0; i < arr->length; i++) {
        printf("%d\n", getNum(arr, i));
    }
    return 0;
}