EnQueue method not returning correctly in C++ circular queue?

Question

I have less than 3 months experience coding, so I've started using LeetCode to just build hours working with code beyond what's assigned in school.

I was working on trying to build a circular queue (FIFO), and it won't compile. I received the following error and I'm stumped:

solution.cpp: In member function enQueue Line 58: Char 2: error: control reaches end of non-void function [-Werror=return-type] }

One thing: I am specifically instructed NOT to use the std::queue library, so while I know that would likely be much easier, it's not an option.

Full code of what I built follows:

class MyCircularQueue
{
private:
    int* data = nullptr;
    int size;
    int capacity;
    int front_p;
    int rear_p;

public:
    /** Initialize your data structure here. Set the size of the queue to be k. */
    MyCircularQueue(int k)
    {
        data = new int[k];
        size = 0;
        capacity = k;
        front_p = 0;
        rear_p = 0;
    }

    /** Insert an element into the circular queue. Return true if the operation is successful. */
    bool enQueue(int value)
    {
        if (!isFull() && isEmpty())
        {
            for (int i = 0; i < capacity; i++)
            {
                if (data[i] == 0)
                {
                    data[i] = value;
                    size++;
                    front_p = data[i];
                    rear_p = data[i];
                    return true;
                }
            }
        }
        else if (!isFull())
        {
            for (int i = 0; i < capacity; i++)
            {
                if (data[i] == 0)
                {
                    data[i] = value;
                    size++;
                    front_p = data[i];
                    rear_p = rear_p++;
                    return true;
                }
            }
        }
        else
        {
            return false;
        }
    }

    /** Delete an element from the circular queue. Return true if the operation is successful. */
    bool deQueue()
    {
        if (isEmpty())
        {
            return false;
        }
        else
        {
            front_p = front_p++;
            return true;
        }
    }

    /** Get the front item from the queue. */
    int Front()
    {
        return front_p;
    }

    /** Get the last item from the queue. */
    int Rear()
    {
        return rear_p;
    }

    /** Checks whether the circular queue is empty or not. */
    bool isEmpty()
    {
        for (int i = 0; i < size; i++)
        {
            if (data[i] != 0)
            {
                return false;
            }
            else
                return true;
        }
    }

    /** Checks whether the circular queue is full or not. */
    bool isFull()
    {
        if (size == capacity)
        {
            return true;
        }
        else
            return false;

    }
};

Answer 1

You're getting that error because the execution thru enQueue does not always end with a return statement. Logically this may never happen but the compiler does not know that, as it sees that if one of the for loops terminates with i >= capacity you won't encounter a return statement.

The simple fix is to remove that last else and so that the return false; will always execute at the end of the function.

    }
    return false;
}