Array of unknown number of elements in c - c

Question

i'm trying to make a game in C, and my problem is this:
I need to have some kind of method in C, that does basicaly what this python code does:
array = list();
len(array) #returns 0
x = 1
array.append(x)
len(array) #returns 1
array.append(2)
len(array) #returns 2
This is just the basic method that I need to do, the test if it's less than 5 is just to be different sizes array, originally my problem is how to manipulate the gunshots in my game, creating them pressing space on the keyboard(appending the gunshot to an until now empty array), and then i have to do something like this, just in C:
for i in range(len(array)):
print array[i]
originally, that's when the loop is running and I have to determine if the gunshot is visible and move it or not, I don't know how to determine the lenght of the array in C, specially if the array has a variable size(can increase size in time)
In Python it would be easy to handle this, but I don't know how to do it in C, and since my game has to be in C 'cause it's for a college class..

Answer 1

I'd suggest a linked list instead of an array, because you'll eventually want to remove arbitrary elements. (Bullet 1 is still travelling across the screen, but bullet 3 hit a wall and bullet 6 hit an enemy.) You can do that directly in your bullet struct rather than as a separate data structure:
typedef struct bullet_t {
/* ...game logic... */
struct bullet_t* next;
} bullet;

Answer 2

C does not support variable sized arrays; if C++ is an option, go for std::vector. If not, you will have to implement that in C on your own. I would personally suggest doing something close to what std::vector does - each time you run out of memory, realloc twice as much.

Answer 3

There are different ways to do what you want to do, but I advice chained list.
Basically, the issue for converting your python code into C-code is the fact that you have to manually allocate your variables most of the time, and here you have. So you can do a chained list, where you allocate every new element with a malloc, and then you link it to the rest of the list with a pointer.
Then, to know the size, just follow the list with a counter.
Good luck. ;)

Answer 4

I would recommend a different ADT. For example a linked list, or a Set ADTs (if you google a bit, you'll probably find finished ones). However, if you absolutely need to use arrays, then you should look up dynamically allocated ones. Here is an implementation example. (Not tested)
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
typedef struct {
int *array;
int size;
int capacity;
} array_t;
#define ARRAY_INIT_CAPACITY 4
array_t *new_array(){
array_t *arr=malloc(sizeof(array_t));
arr->array=malloc(sizeof(int)*ARRAY_INIT_CAPACITY);
arr->size=0;
arr->capacity=ARRAY_INIT_CAPACITY;
return arr;
}
void increase_array(array_t *array){
int new_capacity=array->capacity*2;
int *new_location = realloc(array->array, new_capacity*sizeof(int));
if (!new_location) {
fprintf(stderr, "Out of memory");
exit(1);
}
array->capacity=new_capacity;
array->array=new_location;
}
void array_append(array_t *array, int item){
if (array->size >= array->capacity){
increase_array(array);
}
array->array[array->size]=item;
array->size+=1;
}
int array_size(array_t *array){
return array->size;
}
array_t *myArray=new_array();
I'd recommend learning about dynamic memory allocation and Arrays in C.
Hope it helps :)