Question

Possible Duplicate:
Using Dynamic Memory allocation for arrays

I originally had this program store prices with a quantity size of ten and realized that I wanted to make the program more dynamic because I may need to store more than ten items at some given point. I’m having difficulties understanding on how to reallocate additional memory so that I can store any amount of items I would need. Is this the correct way of handling this task?

main function:

double *purchases = (double*)malloc(QUANTITY_SIZE);

outside function

double startShopping(double *purchases, double *taxAmount, double *subTotal, double *totalPrice)
{
    double itemPrice = 0.00;
    double* storeMoreItems;

    for(int i = 0; i < QUANTITY_SIZE; *subTotal +=purchases[i++])
    {
        while(itemPrice != -1)
        {
            printf("Enter the price of the item :");
            scanf("%lf", &itemPrice); 

            storeMoreItems = (double*)realloc(storeMoreItems, i * sizeof(int));

            if(storeMoreItems != NULL)
            {
                storeMoreItems = purchases;
                purchases[i-1] = itemPrice;
            }

           else
           {
               free(purchases);
           }
       }
  }

  displayCart(purchases);

  *taxAmount = *subTotal * TAX_AMOUNT;

  *totalPrice = *taxAmount + *subTotal;

  printf("\nTotal comes to : $%.2lf\n", *totalPrice);

  return *totalPrice;
}

Answer 1

double* purchases = (double*)malloc(sizeof(double)*QUANTITY_SIZE);

What is more:

storeMoreItems = (double*)realloc(storeMoreItems, i * sizeof(double));

You tried to allocate the i*sizeof(int) and then casted it to double*. When double and int have different sizes your code would have a difficult to find bug.

The next thing:

When i is equal to 0 you allocate memory with initial size 0 bytes (i*sizeof(int)) and then try to use it. It won’t work. Try to change your loop in this way: for (int i = 1, i <= QUANTITY_SIZE;... and keep purchases[i-1].