Question

Having some issues with one small function I’m working on for a homework assignment.

I have a static array size of 20 (shelfSize), however, I only need to use a max of 10 elements. So I don’t have to worry about out of bounds etc (the entire array of 20 is initialized to 0).

What I am looking to do is insert an integer, booknum, into an element of an array it receives as input.

This my current logic:

void insert_at(int booknum, int element){
for(int i=element+1; i < shelfSize; i++)
    bookshelf[i+1]=bookshelf[i]
bookshelf[element]=booknum;
}

so let’s say I have the this array:

[5,4,3,1,7]

I want to insert an 8 at element 1 and have the array turn to:

[5,8,4,3,1,7]

Technically, everything after the final element 7 is a 0, however, I have a separate print function that only prints up to a certain element.

No matter how many times I take some pencil and paper and manually write out my logic, I can’t get this to work.

Any help would be appreciated, thanks.

Answer 1

You should start from the end of the array, this should word for you:

void insert_at(int booknum, int element)
{
    for (int i = shelfsize-1;i>element;i--)
        bookshelf[i] = bookshelf[i-1];
    bookshelf[element] = booknum;
}

Also I recommend that you get used to handling illegal values, for example, what if a user entered 21?

The optimized code would be:

bool insert_at(int booknum, int element)
{
    if (element>=shelfsize-1)
        return false;
    for (int i = shelfsize-2;i>element;i--)
        bookshelf[i] = bookshelf[i-1];
    bookshelf[element] = booknum;
    return true;
}