Sort an array by using function in C++

Question

I want to make a sort statement by using a function. The problem is, I cannot return it back to the main() function. What's the problem? I also tried the void.

int sort_func(int sort[]) {
    int swap = 0;
    for (int i = 0; i < 5; i++) {
        for (int j = 0; j < 4; i++) {
            if (sort[j] > sort[j + 1]) {
                swap = sort[j];
                sort[j] = sort[j + 1];
                sort[j + 1] = swap;
            }
        }
    }
    return sort[5];
}

What is the problem in the code?

Answer 1

You don't need to return anything. The array is being passed into the function via an int* pointer, so the code is directly manipulating the elements of the caller's array.

Also, your 2nd for loop is incrementing i when it should be incrementing j instead.

How is the caller's array declared, exactly? The loops inside your function require the sort parameter to point at an int[] array with at least 5 elements. However, the function's declaration does not convey or enforce that requirement, so the caller is free to pass in however many elements it wants, and if that size is fewer than 5 then your code will have undefined behavior. You should at least have the caller pass in the actual number of elements as another parameter, eg:

void sort_func(int sort[], int size) {
    int swap = 0;
    for (int i = 0; i < size; i++) {
        for (int j = 0; j < (size-1); j++) {
            if (sort[j] > sort[j + 1]) {
                swap = sort[j];
                sort[j] = sort[j + 1];
                sort[j + 1] = swap;
            }
        }
    }
}

int arr[5];
...
sort_func(arr, 5);

Otherwise, if you strictly require 5 elements, then enforce that by taking a pointer to an array with exactly 5 elements, eg:

void sort_func(int (*sort)[5]) {
    int swap = 0;
    for (int i = 0; i < 5; i++) {
        for (int j = 0; j < 4; j++) {
            if ((*sort)[j] > (*sort)[j + 1]) {
                swap = (*sort)[j];
                (*sort)[j] = (*sort)[j + 1];
                (*sort)[j + 1] = swap;
            }
        }
    }
}

int arr[5];
...
sort_func(&arr);

Or, use a reference instead of a pointer, eg:

void sort_func(int (&sort)[5]) {
    int swap = 0;
    for (int i = 0; i < 5; i++) {
        for (int j = 0; j < 4; j++) {
            if (sort[j] > sort[j + 1]) {
                swap = sort[j];
                sort[j] = sort[j + 1];
                sort[j + 1] = swap;
            }
        }
    }
}

int arr[5];
...
sort_func(arr);