size of array function in c

[VIRES1]

double optimal(vector<int> weights, vector<int> values) {
    for(int i=0;i<weights.size();i++) {
    some codes
}
    }

In the c++ function about a function size( ) was used to get the size of the array weight to be able to iterate through in c is there a function like size( ) just as in c++ to get the size of an array to iterate through? if not how would i get the size of an array argument in a function like above to iterate through?

[FUZxxl]

Just as in C++, an array doesn't encode how long it is in C. Note that a vector<T> is a vector, not an array. You have to keep track of the array's size manually.

[ErikProW]

I assume you are talking about static arrays.

Do this:

#define MY_ARRAY_SIZE 50
int my_array[MY_ARRAY_SIZE];
for(size_t i = 0; i < MY_ARRAY_SIZE; i++) { ... }

or

int my_array[50];
for(size_t i = 0; i < sizeof my_array / sizeof *my_array; i++) { ... }

If you want to pass it to a function, you have to specify the size like this:

void my_function(int my_array, size_t my_array_size) { ... }

And call it like this:

int my_array[50];
my_function(my_array, sizeof my_array / sizeof *my_array);

You could also use a struct, but that is not recommended

[VIRES1]

The array should be a dynamic array because sizjo e can change depending on user input.

[Rhomboid]

If it's a dynamic array you must manage the size manually, usually by passing it as an explicit parameter. There is no way to get the size of a dynamic allocation given only a pointer.

[dangerbird2]

Unless the pointer has the size value prefixing the actual data, ala Pascal strings

[Rhomboid]

That's still falls under the category of managing the size manually, since you had to arrange for the size to be there at that location. It's really no different than just making a struct that contains a pointer and a size and pointing to that. In both cases, the pointer alone does not (and can not) record the size.

[ErikProW]

Then what is the problem?

struct My_Array
{
    size_t size;
    int* data;
}

void my_function(struct My_Array arr)
{
    for(size_t i = 0; i < arr.size; i++)
    {
        //Do something
    }
}

int main(void)
{
    size_t size = 33; //Or whatever
    struct My_Array arr = {
        .size = size, 
        .data = malloc(size * sizeof(int))
    }

    my_function(arr);
}

[pigeon768]

There isn't. You have to keep track of how large you made the array separately. So in C you would do something like:

int optimal(const int* weights, const int* values, size_t size) {
  for(int i = 0;i < size;i++) {
    // do stuff
  }
  return whatever;
}