Lesson #1. Introduction to PascalABC.NET

Дата изменения: 17 сентября 2020

Theory

Lection # 1 in pdf format

Variable Definition & Assigning a value to it

  • In Pascal abc.net variables can be defined within the body of the program between begin and end keywords. The principle of locality: a variable is defined immediately before it is used.
  • When we define a variable, we specify its name and type:

  •   
    So we have two possible versions:

  • In traditional pascal:
  • var n: integer; // variable declaration
    begin
      n:=1; // assignment statement
  • pascalAbc.net:
  • 1 method:

    begin
      var n:integer; // variable declaration
      n:=1; // assignment statement

    2 method (canonical method when type is defined depending on the value):

    begin
      var n:=1; // variable declaration and assignment statement => initialization

Arithmetic operations and expressions

    common method:

    begin
      var a := 6; // Assigning value 6
      a:= a + 2; // Increasing by 2
      a:= a - 2; // Reduction of 2
      a:= a * 3; // Multiplication by 3
      a:= a / 2; // division
    end.

    short method:

    begin
      var a := 6; // Assigning value 6
      a+= 2; // Increasing by 2
      a-= 2; // Reduction of 2
      a*= 3; // Multiplication by 3
      a/= 2; // division
    end.

Data input

1-st way:

begin
  var n:integer; // n is a variable of integer type
  read(n); // input some value to store it in n variable
begin
  var n:real; // n is a variable of real type - floating point number
  read(n);// input some value to store it in n variable

2-nd way:

var n:=ReadInteger(); // n is a variable of integer type & we input some value to store it in n
var x:=ReadReal(); // x is a variable of real type & we input some value to store it in x

3-d way (tuple assignment):

var n1, n2: integer; // two integers are declared
(n1, n2) := (1, 2); // 1 is assigned to n1, 2 is assigned to n2

4-th way:

var(n1, n2) := readInteger2; // n1 and n2 are the variables of int type & we input some values to store it in them

Usually before data reading you must print the prompt with an explanation of what data you read:

var x := ReadInteger('Enter x:');
var y := ReadInteger('Enter y:');
var res := x + y;

Data output

1-st way:

begin
  var n:integer;
  read(n);
  n: = n * n;
  writeln('n = ',n);

2-nd way:

begin
  begin
  var n:integer;
  read(n);
  n: = n * n;
  print('n = ',n);

What does formatted output mean?

For beautiful output, you should use formatted output with the WritelnFormat procedure or Print:
1. WritelnFormat:
 

WritelnFormat ('f ({0}, {1}) = {2}', a, b, c);

The result will be:

f (x, y) = z

The first parameter in brackets and single quotes is a format string that specifies the format for outputting expressions.
So, if we want to output:

a + b = b + a = sum

then you just need to replace a, b with {0}, {1}:

WritelnFormat ('{0} + {1} = {1} + {0} = {2}', a, b, x + y)
  • You can specify the width (W) of the output field of the expression N (width in characters): {N,W}. For example, the operator
  • WritelnFormat('x = *{0,5}*', x); // 5 means 5 charecters for displaying x

    works this way:

    x = *    6*
    x = *   -3*
    x = *  123*
    x = *-9876*
    

    2. Print:

    var x := ReadInteger('Enter x:');
    var y := ReadInteger('Enter y:');
    var res := x + y;
    Print($'Sum of {x} and {y} is {res}');

    Swapping Variable Values

    We have:

    var (x,y) := (3,5);


    To do: To swap values of variables:
    Solution 1. Using temporary variable:

    var t := x;
    x := y;
    y := t;

    Solution 2. Using multiple assignment:

    (x,y) := (y,x);
    Two assignments x := y and y := x are carried out simultaneously! Not
    sequentially!

    Labs and tasks

    Follow the rules to make the tasks

    1. Save your files with names as it is given in tasks (e.g. task-04.pas).
    2. Give meaningful names to your variables.
    3. Use comments to make the program clear.
    4. Give the task of the program as a comment before the program code. Use curly braces for comments:
    5. Give the results of your program (log) as a comment after the program code. It’s easy to do just by copying. Use curly brackets to add comments:
    Sample 1:
    To do: Calculate the expression. The values of x, y and z are entered.

     
    The resulting example:

    Input x 
    3
    Input y 
    4
    Input z 
    5
    The result = 1.77800712886037
    

    [Program name: L1sample1.pas]

    ✍ Algorithm (how to do):

    {0.2} Task 1:
    To do: Assign the values to two variables (a=5, b=6). Calculate their average: (a + b)/2. Do this task twice: use different ways of assigning and output.

    Note: it is better to use here formatted output.  

    The resulting example:

    (5 + 6) / 2 = 5.5
    

    [Program name: L1task00.pas and L1task01.pas]

    {0.2} Task 2:
    To do: Assign the values to two variables (a=-0.80, b=-8.0). Calculate the sum, substruction, product and quotient of their squares.
      
    Note 1: To specify a particular number of digits after the floating point you can use format expression of writeln function:

    writeln('result = ', x:5:3) 
    5 means total number of signs to output the number,
     3 means the number of digits to output after floating point.
    

    Note 2: it is better to use here formatted output.

    The resulting example:

    a^2 + b^2 = 64.64
    a^2 * b^2 = 40.96
    a^2 - b^2 = -63.36
    a^2 / b^2 = 0.01
    

    [Program name: L1task02.pas]

    Sample 2:

    To do: The side of a square (variable name is side) is entered. Calculate its perimeter: P = 4·a. Use different methods of assigning, input and output.

     
    The resulting example:

    please enter the side length of a square:
    5.6
    Perimeter P = 22.4
    

    [Program name: L1sample2.pas]

    ✍ Algorithm (how to do):

      1-st way:

      begin
        Writeln('please enter the side length of a square:');
        // Variable declaration to store the value of the side length
        var a := ReadReal;
        var P := 4 * a; // Perimeter calculation
        Writeln('Perimeter P = ', P);
      end.

      2-nd way:

      begin
        Writeln('please enter the side length of a square:');
        // Variable declaration to store the value of the side length
        var a: real;
        readln(a);
        var P := 4 * a; // Perimeter calculation
        Print('Perimeter P = ', P);
      end.
    {0.3} Task 3:

    To do: The side of the square (variable name is side) is entered. Calculate its area: S = a2. Use different methods of assigning, input and output.

    Note: To calculate square of a number you can use sqr() standart function, for example:

    sqrX:=sqr(x);  

    The resulting example:

    please enter the side length of a square:
    2.90
    Area S = 8.41
    

    [Program name: L1task03.pas]

    {0.3} Task 4:

    To do: The sides of the rectangle are entered (a and b). Calculate its area (S = a*b) and perimeter (P = 2 (a + b)).
      
    Note: To specify a particular number of digits after the floating point you can use format expression of writeln function:

    writeln('S = ', S:0:2);
    // :2 means the number of digits to output after floating point

    The resulting example:

    Enter the values of two sides:
    12
    13
    result:
    S = 156.00
    P = 50.00
    

    [Program name: L1task04.pas]

    {0.4} Task 5:

    To do: A diameter of a circle (variable name is d) is entered. Calculate its length (formula L = π·d). The value of π is 3.14. Use different methods of assigning, input and output.
      
    Note 1: π has a constant value. In pascalAbc we can declare constant before the begin section of the program:

    const
      pi = 3.14;
    begin
     // ...
    end.

    Note 2: Make the program using the same style of coding as in sample 2.

    The resulting example:

    please enter a diameter of a circle:
    6.7
    the length of a circle is: 21.038
    

    [Program name: L1task05.pas]

    Sample 3:

    To do: Calculate hypotenuse and perimeter of a right-angled triangle, legs of triangle is entered (square root of (a2 + b2)).

    Note: To calculate square root of a number you can use sqrt() standart function, for example:

    sqrtX:=sqrt(x);  

    The resulting example:

    Input the values of triangle legs:
    3.0
    6.0
    hypotenuse = 6.70820393249937
    perimeter = 15.7082039324994
    

    [Program name: L1sample3.pas]

    ✍ Algorithm:

      Here is an example of right program which is clear for user:
    {0.4} Task 6:

    To do: The length of a cube edge is entered (a). Calculate the volume of the cube (V = a3) and its surface area (S = 6·a2). Give the program log in the form of a comment.
     
    Note: To specify a particular number of digits after the floating point you can use format expression of writeln function:

    writeln('V = ', v:5:3) 
    5 means total number of signs to output the number,
     3 means the number of digits to output after floating point.
    

    The resulting example:

    please enter the side length of a square:
    9.000
    V = 729.000
    S = 486.000
    

    [Program name: L1task06.pas]

    {0.4} Task 7:

    To do: Assign a value to integer variable x (x = 5). Calculate the value of the function:

    y = 4(x-3)6 - 7(x-3)3 + 2
    

     
    Note 1: To calculate the power of a number you can use the power(x:real, y:real) function. For example:

    //2 in the power of 5 =
    powNumb = power (2,5);

    Note 2: It is better to use an auxiliary variable for (x-3)3.

    The resulting example:

    for x = 5 we have y = 202
    

    [Program name: L1task07.pas]

    {0.4} Task 8:

    To do: Calculate the distance between two points with the given coordinates x1 and x2 on the number axis; the coordinates are entered. Formula |x2 − x1|.

    Note: To calculate the absolute value of a number you can use abc(x:real) standart function:

    abs(x2 - x1);

    The resulting example:

    x1 = 3.2
    x2 = 2.5
    the distance between two points: 0.7

    [Program name: L1task08.pas]

    {0.4} Task 9:

    To do: Calculate the distance between two points on the plane; coordinates (x1,y1) and (x2,y2) are entered. The distance is calculated by the formula:

    Note 1:Verify that your program is correct using «simple» values that are easy to calculate. For example:

    d((0,  0); (6, 0)) = 6;   
    d((0,  -4); (0, 1)) = 5;   
    d((-1,  1); (2, 5)) = 5:
    

    Note 2: Display the results of your program (log) in the form of a comment after the program code. It’s easy to do by simply copying. For comments use curly brackets:

    The resulting example:

    enter x1 of the first point:
    0
    enter y1 of the first point:
    0
    enter x2 of the second point:
    6
    enter y2 of the second point:
    0
    The distance equals 6

    [Program name: L1task09.pas]

    {0.3} Task 10:

    To do: The temperature in Celsius is entered, convert temperature to Fahrenheit. Celsius and Fahrenheit scales are related by the ratio:

    and opposite:

    The resulting example:

    please enter the temperature in celsius 
    56
    The temparature in fahrenhiet  132.8

    [Program name: L1task10.pas]

    Swapping Variable Values

    {0.2} Task 11:

    To do: Swap the values of variables A and B and print out the new values to the console.

    The resulting example:

    Enter A: 5.7
    Enter B: 3
    Result:
     A = 3, B = 5.7

    [Program name: L1task11.pas]

    {0.2} Task 12:

    To do: The values of variables A, B, C are entered. Swap their values to make A = B, B = C, C = A, and display the results.

    The resulting example:

    A = 3.4
    B = 2
    C = 1.5
    Result:
     A = 1.5, B = 3.4, C = 2

    [Program name: L1task12.pas]

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