Class 38: Multi-dimensional arrays

Held: Tuesday, 12 April 2011

Summary: We consider multi-dimensional arrays. That is, we consider arrays of arrays. We examine how one declares them, why one might use them, and some complexities in their use.

Related Pages:

• EBoard.
• Lab: Multi-Dimensional Arrays.
• Reading: K&R 5.6-5.9.

Notes:

• Some answer to questions on multi-dimensional arrays posted.
• Missing questions from DG, MH, KI, JTL.
• Really late: AH, JJ.
• No reading for Wednesday!
• I will reserve time at the start of class for questions on on assignment 7.
• More on preregistration: Compilers, Discrete Math, etc.
• EC for either of Tuesday's Town-Hall Meetings on the Forum [academic]
• EC for Thursday's Convocation [academic]
• EC for Thursday's CS Extra [academic]
• EC for Friday's CS Table - Wolfram TED Talk, http://www.ted.com/talks/stephen_wolfram_computing_a_theory_of_everything.html [academic]
• EC for baseball (2 games Saturday, 2 games Sunday) [peer]
• EC for Bob's Benefit Bash Friday [peer]

Overview:

• Multi-dimensional arrays.
• Why?
• Arrays of pointers vs. Arrays of arrays.
• Lab.

Multi-Dimensional Arrays

• You can make arrays of anything.
• Even arrays of pointers and arrays of other arrays.
• What's the syntax for declaring?
• An array of pointers

  TYPE *NAME[SIZE];
  

• An array of arrays

  TYPE NAME[ROWS][COLS];
  

• You can initialize them when declaring.

  char *strings[3] = { "alpha", "beta", "gamma" };
  int stuff[2][3] = { { 1, 2, 3},
                      { 4, 5, 6} };
  

Why Do We Need Multi-Dimensional Arrays?

• When we have arrays of strings.
• When we want to represent matrices for computation (e.g., for those physics types)
• When we want to represent compound data, one way to represent compound data is an array. (E.g., we might represent a student in this class by a five element array of strings: Last name, First name, Student ID, Major, and Grade.)
  • A collection of compound data can then be represented as an array of arrays. (Or, more precisely, an array of arrays of arrays.)
• As you've no doubt determined, tables of numbers are often useful. Two dimensional arrays simultate tables.

Arrays vs Pointers, Revisited

• We've seen that arrays and pointers are similar in some ways, but different in others.
• What's the difference between an array of pointers and an array of arrays?

Lab

• Start The lab.