lab1_report

8/7/2019 lab1_report

1/14

Laboratory course Programming language C++

LABORATORY ASSIGNMENT 1

Report

Lab Objectives

To gain experience with

the activity of programming

using your compiler

the debugger

strategies for effective debugging

Lab check

Please check your status of assignment:

Title Content Cant do it Finished

Pre-lab assignments The Pascal triangle OK In-lab assignments 1. Compiling your file

Debugger

Post-lab assignments Your IDE

1 | P a g e

Name: L HU DUYClass: 08DT2Group: 15BNo.: ????Session: Wed


2/14


Pre-Lab.

The Pascal trianlge

Entries in Pascal's triangle are indexed by integers. n is the number of the row and k is

the position from the leftmost member of the row. The indexes in both directions start at

zero (0), so in the fifth row listed above, C(4,0) = 1, C(4,1) = 4, and so on.

The values themselves are computed by the formula C(n, k) = n! / ( k! (n-

k)!), which is called a combination. n! denotes afactorial, that is, the product n(n-

1)(n-2)...(2)(1). The combinations can be interpreted as the number of ways to

choose k elements from a collection containing n elements. When described, it is

customary to say "n choose k", for instance '4 choose 3 is 4' ".

If 4 objects are numbered 1 through 4, how many ways can you select 2 of them ? Show

all the possible pairings here. Then compute C(4, 2) by using the formula. Does it match

the number of selections?

Your answer

From {a,b,c,d} we have : {a,b} , {a,c} , {a,d} , {b,c} , {b,d} ,

{c,d}

As you will discover with the help of your debugger, the program to compute Pascal's

triangle has some mistakes. Each provides an opportunity to learn a debugging concept in

context of its use.

2 | P a g e


3/14


In-Lab 1.

Compiling and running programs from within your development environment

Frequently in these labs you will be asked to compile a sample program. Below is a copyof a C++ program that displays a drawing. Copy and paste it into your compiler's editor,

and from there save it as art.cpp.

Describe what you did.

Your answer open Code::Block ->file->New->File-> C/C++ emptysource -> next ->c++ ->next -> enter file diriection: D:\project\C++\LAB\art.cpp -> next. Paste codes. SAVE.

#include #include using namespace std;int main()/* PURPOSE: Display an 'art' drawing*/{ string s1 = " * * * * * * ";

string s2 = " * * * * * ";string s3 = "__________________________________\n";string s4 =

"_________________________________________________________\n";

cout


4/14


environment. Find out the steps for your computer system, then go ahead and

compile art.cpp to an executable file.

Describe what you did.

Your answer. Press build button (ctrl +F9)

Finally, execute the program. Once again, the steps depend on your computer system.

Describe what you did to execute the program.

Your answerPress Run ( Ctrl + F10)

Describe what happened when the program executed.

Your answer

In-Lab 2.

The Pascal trianlge

The following portion of the lab is designed to have you practice some of the basics of

debugging. Copy the following program listing into a new file called pastri.cpp on your

hard drive.

4 | P a g e


5/14


/******************************************************************** PROJECT: Lab assignment on debugging* FILE: pastri.cpp* PURPOSE: To compute Pascal's triangle and illustrate* the use of the debugger.* PROGRAMMER: Leslie Foster

* REMARKS: The code below is chosen to illustrate the debugger.* It is neither the most efficient nor the mostreliable* way to solve this problem.*************************************************************************/

#include #include using namespace std;

/*------------------------------------------------------------------*/

void skip(int n)/* PURPOSE: To skip n spaces on a line

RECEIVES: n - the number of spaces to skipREMARKS: n should be non-negative

*/{ int i; /* a counter */

for (i = 0; i


6/14


/* PURPOSE: to calculate the number of combinations of n things takenk at a time (n choose k)

RECEIVES: n - the number of items to choose fromk - the number of items choosen

RETURNS: n choose kREMARKS: n and k must be non-negative and k nrows;cout


7/14


The program's purpose is to display Pascal's Triangle, a sequence of integers that arises in

numerous areas of math and computer science, especially combinatorics and probability.

When completed, the program's output should be:

Enter the number of rows (


8/14


Then set breakpoint at the line int main(void)

Use the Step Into command to restart the program from the very beginning.

Now use the Step Into command several times, until the active line is

cin >> nrows;

Select Step Into again

What happens with the program? Does the Step Into take effect on the following line of

the program?

Your answer : The program permit user to enter the number of rows

Type 5 (followed by the Enter key) for the input. Press Step Into again.

On what line is the cursor positioned now ?

Your answer At D:\project\C++\LAB\pastri.cpp:74

Select your compiler's Memory examine in Debug Windows.

Inspect the value of nrows

How can you do to see value of nrows?

Your answer: debug/debuging windows/Memory examine

What is the value fornrows shown in the dialog box?

Your answer0x22ff0c: 05 00 00 00 70 34 41 00|68 24 2a 00 30 00 00 00....p4A.h$*.0...0x22ff1c: 00 a0 fd 7f 00 a0 fd 7f|00 00 00 00 68 ff 22 00

More stepping

Select Step Outseveral times.

Look at the output for Pascal's triangle.

Does the output have the title: TABLE 1: THE FIRST 5 ROWS OF PASCAL'S

TRIANGLE ?

8 | P a g e


9/14


Your answer Nothing appears

That is strange. The program is supposed to print three newlines, then the title. Let's find

out why the title doesn't appear.

Select Start the to start the debugger once again.

Select Step Into

Then select Step Outuntil you reach the line prompting for input.

Enter 5 for nrows

Select Step Out one more time. This should skip over the

line cout


10/14


Does the title now show up on the screen?

Your answer YES

How many rows of Pascal's triangle are displayed?

Your answer 3

To find out why there are not five rows, return to the source code by pressing

enter.

Select Watches

The variable n is undefined (a random number) because you haven't yet started the

program.

Select Step into several times.

How many lines are now in the watch window?

Your answer : Local variables ; Function Argument;

Resetand Step Into.

Select Step Outuntil you reach the line

skip(spaces_to_skip); /* space to make a triangle */

What values of n and k are in the watch window? (If the watch window isn't presentselect View Watch.)

Your answer n= 0k=4273328

Keep selecting Step Outuntil you are again at the

line skip(spaces_to_skip); /* space to make a triangle */

What are the values of n and k?

Your answer n=2k=1

10 | P a g e


11/14


Keep selecting Step Outuntil you exit the for loops and arrive at the line

cout


12/14


What value does producthave in the inspect window?

Your answer product =4

The reason that productin the inspect window is incorrect is that the line product = product + i;

should be

product = product * i;

Make the above change in your editor.

Recompile

Start andRun the program again with input of 5. Oh no! the triangle is still

wrong!

Setting breakpoints

It is tedious to have to keep stepping to get inside a program. A more efficient way is to

set a breakpoint at a line of interest. Then the program runs at full speed until a

breakpoint is reached.

Startand make sure that n and k are still in the watch window.

Select the line comb = combination(n,k) ;

SelectAdd Breakpoint.

SelectRun until the program stops at the breakpoint. Repeat selectingRun until the watch window displays

n: 3

k: 1

Then Step Into once

and then Step Outuntil you are at the line: return comb;

Select Watches

and follow combfor the expression in the dialogue box.

What is the value listed forcomb?

Your answer

The true value for the combination of 3 things taken 1 at a time is 3! / 1!2! = 6 / 2

= 3. So, the above value ofcombis wrong.

12 | P a g e


13/14


Something must be wrong with our combination calculation. In fact, the

programmer has omitted parentheses in the denominator for the line: comb = factorial(n) / factorial(k) * factorial(n-k) ;

Change the line to be: comb = factorial(n) / (factorial(k) * factorial(n-k)) ;

Recompile and selectResetandRun

Is your Pascal's Triangle correct (for nrows = 5)?

Your answer

Finally

Select the line comb = combination(n,k) ;

Select Breakpoint.

SelectRun

Do the results look OK when you input 13 for the number of rows?

Your answer

They should now. Exit, saving any files you might wish to keep.

13 | P a g e


14/14


Post Lab.

Menu commands and shortcut keys for debuggers

The following table lists commands for debuggers, find out your debuggers commands

and fill in the table to the right.

Feature Button or short keys

Run Ctrl+F10

Step out Shift+Ctrl+F7

Step into Shift+F7

Output screen

Start/ResetWatches

View watches

Breakpoint

14 | P a g e

lab1_report

Documents