How Do You Store All This Data?

Data of all kinds is often stored in arrays to make it easier to work with on a large scale. Arrays are often used in computer programming as a way to store and manipulate data. An example of this data could be the pixels in a two-dimensional image, which is the focus of this lesson. Computer science engineers also know that arrays also make it easier to retrieve stored data.

After this lesson, students should be able to:

• Initialize a two-dimensional array.
• Initialize a new instance of a vector class.
• Store RGB values in a vector.
• Read data from vector and write to a new image.
• Apply new knowledge to the unit's Grand Challenge question.

Tennessee State Standards for C++ Programming Applications (2005)

• Standard 5.0 - The student will write and document an executable program in C++ Programming Language.

Lecture Information

• Two-dimensional arrays are used to store data. Each data point is identified by its horizontal and vertical position in the array. Think of the data as being stored in a grid.
• This address system is similar to the way points on a graph are addressed on an x-y plane, that is, the coordinate points (1, 2) would be one unit from the origin along the x-axis, and 2 units from the origin along the y-axis.

Figure 1. Example 4 x 3 array.

• Similarly, in an array, two subscripts are given, the first standing for the row number, the second representing the column number. By convention, rows and columns are both numbered from 0. Figure 1 shows an example 4 x 3 array and the subscripts representing each point within the array. (Note, the [a][b] notation is unique to C, most other languages refer to the same address as [a,b]).
• The following website explains the use of arrays in computer programming in more detail and gives example coding: https://www.tutorialspoint.com/computer_programming/computer_programming_arrays.htm

Summary

• Two ways to pass a pointer to a two dimensional array: subscript notation and typecasting.
• Subscript notation requires that data type of the second subscript needs to match based on the function.
• Typecasting in the function call uses a pointer with offsets inside the function so that information in arrays of differing dimensions can be processed using the same function.
• A vector template class allows for a dynamic array, which can be expanded to account for input of different amounts of information.

In this lesson, you will learn how a computer image is composed. You will need to understand that a digital image is nothing more than a grid of colors. The grid can easily be stored and manipulated by using nested loops. Following the lesson, students can complete the associated activity Putting It All Together: Programming Robotics Peripheral Vision.

As homework, have students complete the Data Storage Assignment Handout (PDF), which asks them to read data from a 16 x 16 image grid and store the data in an array. Then they are challenged to see if they can flip the image around by using nested loops. Assess their learning by their completion of the 16 x16 grid manipulation code and answers to the handout questions. Then proceed to conduct the associated activity, Putting It All Together: Programming Robotics Peripheral Vision.

"Array." Dictonary.com. Unabridged. Random House, Inc. Accessed 22 Jun. 2010. http://dictionary.reference.com/browse/Array