Programming Taskbook

Russian

1000 training tasks on programming

©  M. E. Abramyan, 1998–2011

Solution of the simple task: Begin3

This section contains description of solving the following simple task in Borland Delphi:

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.

Creating a template and acquaintance with the task

To create a template of the required task one should use PT4Load tool.

The template created for Delphi environment consists of Begin3.dpr file that contains the following text:

{$D+,L+,I+,Q+,R+,S+}
program Begin3;
uses PT4;

begin
  Task('Begin3');
end.

The first statement is compiler directives (among them there are input-output checking {I+}, overflow checking {Q+}, and range checking {R+}). The statement with uses clause add the PT4 module to the program. The last statement is the Task procedure call that initializes the Begin3 task.

To run the program press [F9] key. When the program is launched you will see the Programming Taskbook 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 {F9] key.

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 procedure (the line of compile directives and the PROGRAM statement will not be show for brevity):

uses PT4;
var
  a, b: integer;
begin
  Task('Begin3');
  GetN(a);
  GetN(b);
end.

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."

To input data correctly we should use the GetR procedure that provides input data of real type. Change our program as follows:

uses PT4;
var
  a, b: real;
begin
  Task('Begin3');
  GetR(a);
  GetR(b);
end.

Now data input is performed correctly, but the program does not output results. Therefore we have the following message: "Some data are not output.".

Calculation and output results

Let's perform the required calculations and output results using the PutR procedure:

uses PT4;
var
  a, b, S, P: real;
begin
  Task('Begin3');
  GetR(a);
  GetR(b);
  S := a * b;
  P := 2 * (a + b);
  PutR(P);
  PutR(S);
end.

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:

  PutR(S);
  PutR(P);

When this program is running you will see the following information in the status bar: "Right solution. The test 1 of 3".

We have performed successfully the first test of our program. But the correctness of the algorithm must be proved by a number of tests with various initial data. The amount of tests is in range from 3 to 9 and depends on the level of the task difficulty (for the Begin3 task it is enough 3 tests). If all required tests are performed successfully then the message "The task is solved!" will be shown at the status bar. If some test is failed then the algorithm should be corrected and tested again.

In our case the algorithm is correct, therefore the message "The task is solved!" will be shown after 3 test runnings.

To browse information about the task solving you can use PT4Results tool.

Remark. It is not necessary to use additional variables S and P, because you can output expressions:

uses PT4;
var
  a, b: real;
begin
  Task('Begin3');
  GetR(a);
  GetR(b);
  PutR(a * b);
  PutR(2 * (a + b));
end.

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

Last revised:
04.06.2011