7.5 Passing Arrays to Functions

Tricky but necessary.

7.6 Case Study: Class GradeBook Using an Array to Store Grades

Study.

7.7 Searching Arrays with Linear Search

A very common algorithm -- study in detail. Think how you might adapt it to your own programming projects.

7.8 Sorting Arrays with Insertion Sort

Remind me to demonstrate this in class with my pack of magician's cards.

7.11 Introduction to C++ Standard Library Class Template vector

Review vectors -- remember: they are more powerful but slower to use than arrays.

. . . . . . . . . ( end of section Prepare) <<Contents | End>>

Deliver a question

This class is intended to store a sample data: a set of real numbers and calculate as needed various statistics: min, max, mean, standard deviation (sd). Because the data and the functions are placed in a class a program can declare and use many different Samples -- and, for example, calculate correlations between them.

See [ lab10/ ] for a starter class and test program.

Questions and Answers

Which companies use sorts

All people need there data sorted and so use sort programs. This is why we study them in Computer Science. Example: A phone company lists its subscribers in a phone book that is sorted.

Why not use insertion sort for long arrays

Try it with a deck of cards and see:-)

When to use Insertion sort

A rule of Thumb: No more than 10 items!

Because for more than 10 items there are faster ways to sort them. Covered in CS202 and CS330.

Why is insertion sort simple but not efficient

Like most simple things -- it is not as good as some clever algorithms -- especially when there is lots of data. More in CS202.

Please give more details on the STL vector template class

First check out [ samples/stl.html#Vectors ] then check out SGI's site [ http://www.sgi.com/tech/stl/ ] then look in the standard [ ../c++std/cd2/lib-containers.html ] (tough going but complete).... and then hit the library!

Why doesn't vector at return an rvalue

All lvalues are coerced to rvalues when an rvalue is needed.

What is an lvalue and an rvalue

When a variable appears on the left of an assignment

 		left = right;

it is an lvalue -- a place where data can be put. lvalues are places to store data. On the other side (right) the variable is used as supplying a value -- this is an rvalue -- a place or expression that gives a value. Lvalues are places and rvlaues are things in those places.

How come linear search is bad for large arrays

It becomes very slow with lots of data to search. Remember finding the name of the person with number 123-4567 in a normal phone book. This requires a linear search and will take hours if not days. Finding "Victor Hugo" in a normal phone book is much quicker because we don't use linear search.



What is a template vector

It is a long name for a vector.

What is a template

A template class or function is written to have some unknown types of data and adjusts to the data you supply.

vectors are template classes.... Hence "vector <....>"

How often are vectors used in C++

A lot!

The modifyArray function on page 356 has a parameter sizeOfArray -- does it change the size of the array

Nothing can change the ammount of space you give to an array when you declare it. NOTHING!

In this function you can input any number as the size. You can lie! But this may not be wise.

If the parameter has a value bigger than the real size then the function can do just about anything to your program.... upto and including shutting down the computer, by way of strange bugs and errors.

If the parameter is equal to size of the array then all should be well.

If the parameter is less than the real size the function will probably only use part of the array. And this may be what you wanted.

How are arrays passed by reference

The formal parameter gets the address of the first item in the array (item [0]). In the function the items are found by cacultaion, of course:

 		item[i]

 		address of item + (i * sizeof item).

The function gets the size from the parameter type.

Thus it can get to any element in the original array.

If an array is associated with a const parameter can it ever be changed

Not by the called function. Other parts of the program can still change it.

When to use const for local variable

When they are constants! Good examples are π, Euler's e, Avogadro's number, Days in Week, Months in year, and so on.

Are arrays the only things passed by reference by default

Yes. In C++ objects are copied and elementary data are copied in unless you use the "&" in the parameter specification.

Can we have unsigned subscripts for vectors

Yes... but they will be converted to signed.

What is in the final

[ mock2009.html ]

Questions about the Big-O notation

Will be answered in [ cs202/ ]

How to use elements of an array as counters

With arrays you need a fixed number. Suppose we have some events that happen at different days.... and to count how many in each month....

 		const int MONTHS =12;

 		int counter[MONTHS]={};

 		//some kind of loop

 			//Calculate a month...

 			counter[ month ] ++;

 		//end the loop some how

Something like the above should work.

Next -- Review Course Content