Worksheet 14: Introduction to Dynamic Arrays Name:
An Active Learning approach to Data Structures using C
1
Worksheet 14: Introduction to the Dynamic Array
In Preparation: Read Chapter 5 to learn more about abstraction and the basic abstract
data types, and the dynamic array as a n implementation technique.
Suppose you want to write a program that will read a list of numbers from a user, place
them into an array and then compute their average. How large should you make the
array? It must be large enough to hold all the values, but how many numbers will the user
enter? A common solution to this difficulty is to create an array that is larger than
necessary, and then only use the initial portion. This is termed a partially filled array.
When you use a partially filled array there are two integer values of interest. First is the
array length. When discussing partially filled array this
is sometimes termed the capacity of the array. Second is
the current size, that is, the amount of the array that is
currently being used. The size is generally maintained
by a separate integer variable. If we place the values into
a structure it will be easier to keep them together.
It is important to not confuse the size and the capacity. For example, in computing the
sum and average you do not want to use the capacity:
double average (struct partFillArray * pdata) {
double sum = 0.0;
int i;
for (i = 0; i < 50; i++) /* Error–loop using length */
sum = sum + pdata->data[i]; /* Error-uninitialized value */
return sum / 50; /* Error–average is under estimated */
}
Instead, you want to use the size:
double average (struct partFillArray * pdata) {
double sum = 0.0;
int i;
for (i = 0; i < pdata->size; i++)
sum = sum + pdata->data[i];
return sum / pdata->size;
}
struct partFillArray {
double data[50];
int size;
};
