Sections 0101, 0102, 0103 and Honors, Fall 1995

Thursday November 30, 1995

Assigned Reading: 13.5 - 14.3

Handouts (available on-line): none

Topics Covered:

• For fun: a very unclear program which produces an interesting output. Unfortunately the author of the program misspelled "eighth" as "eigth" in this program. Just imagine having to figure out how to correct the program!

• We continued looking at dynamicaly changing the number of elements in an array. In our third example, we want to allow the user to enter a list of positive numbers and use -1 to indicate the end of the list. In this case, we do not know ahead of time how large to make the array. Our strategy is to first allocate an array of 10 elements. If the user enters more than 10 elements, we allocate an array with 20 elements and copy the first 10 elements into the new array. We proceed with this strategy and double the size of the array every time the user exceeds the size of the current array. We double the size of the array because this is much faster than increasing the size of the array by 1. See Program and sample run.

• In our fourth example of memory allocation, we use the NewArray and FreeBlock functions from the course library instead of malloc and free. These functions do the error checking for you. We allocate a 27 character array to store the letters of the alphabet followed by the null character '\0'. This character signals the end of a string. In fact, the strings we have been using all along are really pointers to dynamically allocated arrays of characters. Thus, at the end of the program we can print out the characters in our array using %s. Program and sample run.

• Knowing that strings are really dynamically allocated arrays allows us to access the elements of the array and change them directly. For example, we can now write an implementation of the Captain Crunch secret decoder ring much easier. Program and sample run.

• Also we now have more efficient ways to examine every character in a string. The following program shows three ways of translating each character in a string to upper case. They all do the same thing, but some of the methods are much slower. Program and sample run.

• We discussed how the course's string library handles memory allocations for strings.