Range within an array in C

Question

I came up with an algorithm and I wanted to ask something. Is there any way to set a range of values within an array?

Eg

int N = 10;
int array[N] = {2,6,5,9,4,3,5,9,4,9};

and using a loop to increase the start value with each pass.

for (int A = 1; A < N - 2; A++) {
    for (int B = 1; B < N - 1; B++) {
        int ProfitA = Sum(array[0...A-1]);
        int ProfitB = Sum(array[A...A+B-1]);
        int ProfitC = Sum(array[A+B...N-1]);
    }
}

So is there any way to set the range of values in each array using the above C -pseudocode?

Answer 1

No, C does not have such functionality built in. Moreover, there is no functionality to get the upper boundary of an array once you pass it to a function (so called "decaying to pointers").

There are two standard solutions to this problem:

• Pass a pointer to the first array element and the count of elements, or
• Pass a pointer to the whole array, an index to the initial element, and an index to the last element

The first approach would look like this:

int sum_array(int* array, size_t len) {
    int res = 0;
    for (size_t i = 0 ; i != len ; i++) {
        res += array[i];
    }
    return res;
}
...
int ProfitA = sum_array(array, A);
int ProfitB = sum_array(array+A, B);
int ProfitC = sum_array(array+A+B, N-A-B);

the second approach would look like this:

int sum_array(int* array, int first, int last) {
    int res = 0;
    for (int i = first ; i <= last ; i++) {
        res += array[i];
    }
    return res;
}
...
int ProfitA = sum_array(array, 0, A-1);
int ProfitB = sum_array(array, A, A+B-1);
int ProfitC = sum_array(array, A+B, N-1);