Chapter 9: Pascal Standard Libraries

Pascal comes with several standard libraries, also called units, that cover a wide range of tasks, from basic input/output to mathematical computation and string manipulation. Knowing them saves you a lot of work and lets your programs do more. This chapter covers some of the most commonly used ones: crt, SysUtils, and Math.

The CRT unit

The crt unit has functions and procedures for console input and output and for managing the screen.

Including the CRT unit

To use the crt unit, include it in the uses clause of your program.

uses crt;

Clearing the screen

begin
  ClrScr;
  writeln('Screen cleared!');
end.

Moving the cursor

begin
  GotoXY(10, 5);
  writeln('Cursor moved to position (10, 5)');
end.

Changing text color

begin
  TextColor(Red);
  writeln('This text is red.');
  TextColor(White);
end.

Pausing the program

begin
  writeln('Press any key to continue...');
  ReadKey;
end.

The SysUtils unit

The SysUtils unit has system-related utilities for string manipulation, file handling, date and time operations, error handling, and more.

Including the SysUtils unit

Add the SysUtils unit to the uses clause of your program to use it.

uses SysUtils;

String manipulation

Converting strings to numbers

var
  str: string;
  num: integer;

begin
  str := '123';
  num := StrToInt(str);
  writeln('Converted string to integer: ', num);
end.

Converting numbers to strings

var
  num: integer;
  str: string;

begin
  num := 456;
  str := IntToStr(num);
  writeln('Converted integer to string: ', str);
end.

File handling

Checking if a file exists

var
  fileName: string;

begin
  fileName := 'test.txt';
  if FileExists(fileName) then
    writeln('File exists.')
  else
    writeln('File does not exist.');
end.

Deleting a file

var
  fileName: string;

begin
  fileName := 'test.txt';
  if DeleteFile(fileName) then
    writeln('File deleted.')
  else
    writeln('Failed to delete file.');
end.

Date and time operations

Getting the current date and time

var
  currentTime: TDateTime;

begin
  currentTime := Now;
  writeln('Current date and time: ', DateTimeToStr(currentTime));
end.

Don’t name the variable now. Pascal ignores case, so a variable called now hides the Now function, and now := Now would copy the uninitialized variable into itself instead of reading the clock.

Formatting date and time

var
  currentTime: TDateTime;

begin
  currentTime := Now;
  writeln('Formatted date: ', FormatDateTime('yyyy-mm-dd', currentTime));
  writeln('Formatted time: ', FormatDateTime('hh:nn:ss', currentTime));
end.

The Math unit

The Math unit has mathematical functions and constants.

Including the Math unit

As with the other units, list Math in the uses clause of your program to use it.

uses Math;

Common mathematical functions

Calculating the square root

var
  x, result: real;

begin
  x := 16.0;
  result := Sqrt(x);
  writeln('Square root of ', x:0:2, ' is ', result:0:2);
end.

Sqrt is built in: it comes from the System unit, which every program uses automatically, so this example works without uses Math.

Calculating the power of a number

var
  base, exponent, result: real;

begin
  base := 2.0;
  exponent := 3.0;
  result := Power(base, exponent);
  writeln(base:0:2, ' raised to the power of ', exponent:0:2, ' is ', result:0:2);
end.

Constants

Mathematical constants

begin
  writeln('Value of Pi: ', Pi:0:10);
end.

Like Sqrt, Pi is built into the System unit. The Math unit adds constants such as Infinity, NaN, and MaxFloat.