CS Week 14 Lab Exercise

Transcription

1 CS Week 14 Lab Exercise p.1 Deadline CS Week 14 Lab Exercise Due by the end of lab on (Submit whatever you have by the end of lab, even if incomplete.) How to submit Submit your.cpp file for this lab on Purpose To practice with while loops and arrays. Important notes You are required to work in pairs on this lab exercise. If you are not pair-programming, then you may not receive full credit for your lab exercise. If there are an odd number of students attending lab, one team (and one team ONLY) may have 3 students. TYPE BOTH OF YOUR NAMES in the beginning comment of your.cpp file! To Start: BEFORE YOU START UP NetBeans!!!, LOG INTO your/your partner's G: drive! Look for the large ^ on the lower-right corner of your lab computer's screen Click on that, and click on the drive icon (with a triangular logo), and log in NOW start the NetBeans software. From the File menu, select New Project.... Select Category C/C++ and Project C/C++ Application, and click Next>. Type lab14 in the Project Name box, and use Browse... to direct the Project Location folder to your G: drive. If you wish to create or navigate to a particular folder within your G: drive, do so. If you would like to rename the.cpp file to be a name other than main.cpp, you may do so. All other options should remain as they are. Then select "Finish". In the left-side window, expand the Source Files section, then double-click on main.cpp or the.cpp file name you chose this should open an editor window with the contents of that.cpp file. REPLACE its initial contents with the "first main.cpp contents" from the CS 111 public course web site, under "References". Put BOTH of your names in the by: comment, along with today's date!

2 CS Week 14 Lab Exercise p.2 Problem 1 The purpose of this problem is to practice with writing a function containing a count-controlled while loop. For review: consider example functions cheer, sum_pos_int, and vertical, from the posted Week 12 in-class examples. All of these functions used a while loop to help to do their tasks. In the "first main.cpp template" you pasted into your main.cpp, find the comment: /*--- PUT YOUR SIGNATURES, PURPOSES, and FUNCTION DEFINITIONS HERE ---*/ After this comment, type a blank link, and then type the comment: Problem 1 Using the design recipe, design and write a function starline that: expects a desired number of asterisks/stars to print to the screen, has the side-effect of printing to the screen that many asterisks on a single line, followed by a newline character, and then returns the number of asterisks/stars printed to the screen. (If an integer that is <= 0 is given, no asterisks should be printed, and it should return 0, since no asterisks were printed. BUT it should still print a newline to the screen in this case.) Because this function has a side-effect, we need to describe the expected side-effect for each of its tests -- so, for each of its examples/tests to be run in the main function: you should first print a message saying that what follows should be a line containing <desired number> asterisks, followed by true, and then put that example/test in its own separate cout statement, such that the result of that test will be printed on its own line. Make sure your program runs, and its tests pass! Problem 2 Now go down to your main function. AFTER your tests for Problem 1's starline, IN your main function, put: Problem 2 Array review, plus a little more: Recall, from the Week 12 lecture 2 projected notes: you declare a C++ (statically-allocated) array using the syntax: <array_elements_type> <array_name> [ number_of_elements ]; so, for example: int grades[10]; // grades is an array of 10 ints

3 CS Week 14 Lab Exercise p.3 string cities[20]; // cities is an array of 20 strings double wts[15]; // wts is an array of 15 doubles THEN, if you wanted to, for example, set everything in the newly-declared wts array to 0, you could do so with this code fragment (remembering that array indexes START at 0, and go to ONE LESS than the number of elements in the array): int index = 0; while (index < 15) wts[index] = 0; index++; Of course, if we have a constant number of weights, using a named constant for the wts array's size would be better style! That is: const int NUM_WTS = 15; double wts[num_wts]; int index = 0; while (index < NUM_WTS) wts[index] = 0; index++; ADDITIONAL new array fun fact: if your array is pretty small, you can initialize it WHEN you declare it using the syntax: <array_elements_type> <array_name> [ number_of_elements ] = For example, expr1, expr2,... expr_size_minus_1; const int NUM_FLAGS = 3; bool flags_so_far[num_flags] = true, false, true;...would result in flags_so_far[0] being set to true, and flags_so_far[1] being set to false, and flags_so_far[0=2] being set to true. YOUR Problem 2 actions: (Remember, you are doing the following in your main function, AFTER starline's tests!) SO: To practice declaring and filling and using an array: decide on a desired topic for a set of strings (songs, movies, sports teams, game characters, etc.) declare a named constant of type int for how many things of that topic you would like in an array you are about to create. (It needs to be 4 or greater, and be sure to give it an appropriate descriptive name!) declare an array of type string whose size is that named constant you just created, and, again, be sure to give it an appropriate, descriptive name.

4 CS Week 14 Lab Exercise p.4 initialize its values to appropriate values based on its chosen topic. print to the screen a message on its own line giving the topic of YOUR array. and finally write a while-loop that uses your named constant to repeat that many times, which uses your array and prints each of its elements to the screen on its own line. Problem 3 After Problem 1's starline, (BEFORE your main function), type a blank link, and then type the comment: Problem 3 INFO YOU NEED for PROBLEM 3: Now: you need to know a few more things to be able to write a function with an array parameter: A C++ array does not "know" its size! You know the size you declare it to be, but if you pass an array to a function as an argument, that function does not know how many items are in it! SO: it is considered GOOD STYLE in C++, whenever you have an array parameter, to ALSO have a parameter that is how many items are IN that array! How do you indicate, in a function signature, if a parameter's type is an array? Write the type of element that array will hold, followed by [ ]. So, if you want a function sum_array that expects an array of double values and its size, and returns the sum of the elements in that array, you would have the signature: // signature: sum_array: double[] int -> double You know how to declare an array as a local variable: const int NUM_VALS = 5; double my_list[num_vals] = 10, 20, 3, 4, 100; But, how do you declare an array parameter? Here is one common way: array_type parameter_name[] (that is, you put the type of the parameter array, its name, and then an EMPTY set of square brackets) So, the function header for sum_array could be: double sum_array(double values[], int values_size) And, how can you then pass an array as an argument to a function expecting an array parameter?...you give JUST the name of the argument array! So, if you had the local named constant and local variable: const int NUM_VALS = 5; double my_list[num_vals] = 10, 20, 3, 4, 100;...then you could print to the screen the result of calling sum_array with the array my_list with the statement:

5 CS Week 14 Lab Exercise p.5 cout << sum_array(my_list, NUM_VALS) << endl; YOUR Problem 3 actions: SO -- for this problem, you will walk through the design recipe to create this function sum_array. Whichever you choose, now do the following: Write the signature comment for sum_array: /*--- * signature: sum_array: double[] int -> double Write the purpose statement comment for sum_array: * purpose: expects an array of numbers and returns * its sum. If the array is empty, return 0. Write the function header for sum_array (after the still-in-progress opening comment): double sum_array(double values[], int values_size) Write at least two sets of examples/tests for sum_array -- since it needs an array argument, you will need to include an example argument array declaration for each example: That is, examples/tests for sum_array could be written (back inside the opening comment) as: * tests: * for: * const int NUM_VALS = 5; * double my_list[num_vals] = 10, 20, 3, 4, 100; * then: * sum_array(my_list, NUM_VALS) == 137 * for: * const int NUM_BIRDS = 4; * double my_bird_wts[num_birds] = 25.0, 16.3, 10.0, 1.7; * then: * sum_array(my_bird_wts, NUM_BIRDS) == 53.0 and in the main function testing sum_array, you would need declare these example arrays, also -- you would need something like: cout << "*** Testing sum_array ***" << endl; const int NUM_VALS = 5; double my_list[num_vals] = 10, 20, 3, 4, 100; cout << (sum_array(my_list, NUM_VALS) == 137) << endl; const int NUM_BIRDS = 4; double my_bird_wts[num_birds] = 25.0, 16.3, 10.0, 1.7; cout << (sum_array(my_bird_wts, NUM_BIRDS) == 53.0) << endl; Finally, implement sum_array's function body: double sum_array(double values[], int values_size) double sum_so_far = 0.0; int index = 0;

6 CS Week 14 Lab Exercise p.6 while (index < values_size) sum_so_far += values[index]; index++; return sum_so_far; Make sure your function sum_array runs, and its tests pass. Problem 4 After Problem 3's sum_array, (before your main function), type a blank link, and then type: Problem 4 Now use the design recipe to write a function print_all, described below. print_all expects an array of double values and its size, and returns the array's size, but has the sideeffect of (using a while loop to) print to the screen the contents of that array, one array element per line, with each element preceded by its array index, a colon, and a blank -- that is: const int NUM_ACCTS = 4; double curr_bills[num_accts] = 13.34, 5.61, , 56.12; print_all(curr_bills, NUM_ACCTS) == NUM_ACCTS...and would cause the following to be printed to the screen: 0: : : : And: const int NUM_WIDGETS = 6; double widget_costs[num_widgets] = 2.99, 3.99, 1.99, 0.99, 0.99, 13; print_all(widget_costs, NUM_WIDGETS) == NUM_WIDGETS...and would cause the following to be printed to the screen: 0: : : : : : 13 Then, to test this, in your main function, call print_all at least THREE times, for three DIFFERENT arrays, preceding each call with a description of what should be seen. (Why three? For more practice declaring and initializing an example array "on your own", in addition to likely using the two example arrays given above.) Make sure your function print_all runs, and its tests pass.