Programming Taskbook


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1100 training tasks on programming

©  M. E. Abramyan (Southern Federal University), 1998–2022

 

Examples | C++ | Simple task

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Solution of the simple task: Begin3

This section contains description of solving the following simple task in C++:

Begin3°. The sides a and b of a rectangle are given. Find the area S = ab and the perimeter P = 2(a + b) of the rectangle.

We shall use Visual Studio 2017 as programming environment, however the same results may be received in the other C++ environments that are supported by Programming Taskbook: Visual Studio 2019, 2022, Code::Blocks, Dev-C++, VS Code.

Creating a template and acquaintance with the task

To create a template of the required task you should use the PT4Load tool (starting with version 4.22, you can use the PT4Panel tool for quick launch of all Programming Taskbook tools; the PT4Panel shortcut is located on the desktop and in any working directory).

The template created for Visual Studio 2017 consists of several files. But we need only Begin3.cpp file. This file will be loaded into the code editor of Visual Studio:

#include "pt4.h"
using namespace std;

void Solve()
{
  Task("Begin3");
}

The file contains the definition of the Solve function, which the solution of the task should be entered in (of course any other functions may be used). The Solve function already contains the Task function call that initializes the Begin3 task.

Note that a header file named pt4.h is included in the Begin3.cpp file. It contains declarations of additional types and functions, in particular, the Get–Put functions. Definitions of these functions are contained in the pt4.cpp file. The pt4.h file also contains a definition of the WinMain function, which calls the Solve function. These files are not loaded into the editor of Visual Studio. But the project includes the pt4.h and pt4.cpp files (see the Solution Explorer window located on the Visual Studio window).

To run the program, press [F5] in Visual Studio or Visual Studio Code, [F9] in Code::Blocks, [F11] in Dev-C++. Before compilation of the program, the Visual Sudio environment may output the following dialog box

Select "Yes" (it is enough to press [Enter]). When the program is launched, you will see the Programming Task window with a task text and initial data.


This running is considered as acquaintance running because the program does not perform input-output operations. To close the Programming Taskbook window, click the Exit button or press [Esc] (or [F5] in Visual Studio or Visual Studio Code, [F9] in Code::Blocks, [F11] in Dev-C++).

Initial data input

Before solving tasks you should input initial data in the program. In the Begin3 task the initial data are real numbers a and b that refer to sides of the rectangle.

The initial data should be input in the variable of the required type, otherwise Programming Taskbook will detect error. Let's model this situation in our program. For this purpose we shall organize initial data input to variables of the integer type using the GetN function:

void Solve()
{
  Task("Begin3");
  int a, b;
  GetN(a);
  GetN(b);
}

Run the program once again. You will see the new set of initial data. For each running of the program a new initial data are generated, so it is necessary to develop an algorithm that processes correctly all admissible sets of initial data.


In this case the running leads to the following information in the status bar: "Invalid type is used for an input data item." Note that each type of errors is marked by different color.

To input data correctly we should use the GetD function that provides input data of double type. Change our program as follows:

void Solve()
{
  Task("Begin3");
  double a, b;
  GetD(a);
  GetD(b);
}

Now data input is performed correctly, but the program does not output results. In such situation we have the following message: "Correct data input: all required data are input, no data are output" (Programming Taskbook version 4.15 or higher) or "Some data are not output" (previous versions).

Calculation and output results

Let's perform the required calculations and output results using the PutD function:

void Solve()
{
  Task("Begin3");
  double a, b;
  GetD(a);
  GetD(b);
  double S = a * b, P = 2 * (a + b);
  PutD(P);
  PutD(S);
}

When the program is running you can see output values at the panel of results. Because we output data in inverse order, the status bar contains the error message "Wrong solution".


Right solution and its testing

To correct the last error it is enough to change order of two output statements in the Solve function:

  PutD(S);
  PutD(P);

When this program is running you will see the testing panel on screen:

This panel appears when the program processes successfully at least one set of input data. The progress bar shows the amount of tests which are already performed, the text above the bar allows to determine how much tests should be performed successfully. The program testing finishes in two cases: when all required tests are performed successfully or when some test is failed. If the program is in infinite loop then you should close the testing panel by means of the [x] button in its upper right corner.

In our case the algorithm is correct, therefore the message "The task is solved!" will be shown.


To browse information about the task solving, you can use PT4Results tool (you may run this tool by pressing the [F2] key or clicking the Results label in the upper-right corner of the Programming Taskbook window):

Begin3      c23/02 20:13 Acquaintance with the task.
Begin3      c04/02 15:07 Invalid type is used for an input data item.
Begin3      c04/02 15:09 Correct data input.
Begin3      c04/02 15:12 Wrong solution.
Begin3      c04/02 15:15 The task is solved!

The letter "c" denotes the programming language being used (C++).

Remark. With using the special pt stream we can make the program text more short:

void Solve()
{
  Task("Begin3");
  double a, b;
  pt >> a >> b;
  pt << a * b << 2 * (a + b);
}

Since version 4.15, the pt stream can be used in conjunction with iterators ptin_iterator<T> и ptout_iterator<T> to arrange input and output sequences.

Since version 4.22, one can also use the GetBool, GetInt, GetDouble, GetChar, and GetString functions to input data. Applying the GetDouble function, we can get a Begin3 solution consisting of just two statements:

void Solve()
{
  Task("Begin3");
  double a = GetDouble(), b = GetDouble();
  pt << a * b << 2 * (a + b);
}

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Designed by
M. E. Abramyan and V. N. Braguilevsky

Last revised:
19.04.2022