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Guide to Data Types in Pascal

Updated on February 19, 2013
Lazarus is a popular free, open-source IDE for Delphi and Pascal
Lazarus is a popular free, open-source IDE for Delphi and Pascal

Why Learn Pascal?

Pascal is considered an old, long-dead computer language by a lot of people. However, it is still recommended and thought in a lot of schools and elementary courses. This is because it is a great language to learn how programming works and it gives you a solid education so that you can continue to learn other language later.

Learning Pascal will also help you master Delphi which is an object-oriented language in which you can create your first desktop applications, games and useful tools and software. This article isn't a guide in which you will learn how to program, but will give you some basics and will teach you a lot about the many different data types in Pascal.


In mathematics we often use Z to categorize that a number belongs to the predefined type we know as Integers. In this set we have numbers ranging from [-∞...-4, -3, -2, -1, 0, 1, 2, 3....+∞]. As you can see an integer is either a negative or positive whole number or zero.

Numbers such as 5.55, 3.3333... or the square root of 2 are not integers.

Integers in Pascal

Size in Bytes
0 .. 255
Short Integer (Shortint)
-128 .. 127
Small Integer (Smallint)
-32768 .. 32767
Either smallint or longint
2 or 4
Long Integer (Longint)
-2147483648 .. 2147483647
-9223372036854775808 .. 9223372036854775807

Using Integers - an example

project FirstProgram;

a,i,sum: Integer;  //declaring three integer variables

sum:=0; //starting value of 'sum'
readln(a); //user inputs the value for the variable a

for i:= 1 to a do //a for loop from 1 to a
 sum:=sum+i;  //calculates the sum of all numbers from 1 to a


writeln(sum); //result output

Real Numbers / Floats

We saw that Integers were whole numbers, but what happens when we want to have a numbers such as 1.25 or even 3.333333...? Storing these numbers into a computer's memory used to be quite tricky, especially if they were an infinite array of numbers. Thus, a new data type was created - floating numbers -> float or as they are called in Pascal -> Real. This data type is used to display rational numbers that will probably have a decimal points and/or an exponent. As with the Integer data type, there are several Real types in Pascal with a different range and different memory requirements.

Real Data Type

Size in Bytes
Platform dependent
4 or 8
1.5E-45 .. 3.4E38
5.0E-324 .. 1.7E308

Using Real - an example

program SphereVolume;

  v,r:real;        //volume and radius as real data types

  read(r); //input radius
  v:=(r*r*r*Pi*4)/3; //calculate volume; 
   // Pi is a constant with a value of 3.14

  writeln(v); //output

Characters and Strings

Characters and string come in many different data types and they can be very complex. There also many operation and functions you can do with them which opens up a lot of possibilities for a creative programmer. If you starting out, it is important to note that these data types represent ASCII characters. This means that if you had, let us say, a variable S that was string that had the value of '24' you could not use this variable for mathematical operation as this neither an integer not a real data type.

Chars and Strings in Pascal

A single ASCII char
255 ASCII chars
No limit
0 .. 255 (max) ASCII chars

Using chars and strings in Pascal - an example

program Changingastring;

  C:Char; // a single character 
  S:String; //our string

  S[n]:=C; //


Explanation of the above code

Strings work as a sort of array of characters and we can modify each element individually if we so desire. For example:

Our String S is 'ABCDEF' and has 6 characters in it. If we told our program:


This would output the letter "C". In the code above we input a character, a number and a String. Then we replace the a character in the string that has the position n with the character C.


Input: +, 4, ABCDEF

Output: ABC+EF

Boolean Data Types

I saved what I find the easiest of the elementary data types for last and this is Boolean. This data type requires only one byte and can either be True or False. Bellow is a code that will, hopefully, explain this in more detail.

Using Boolean in Pascal - an example

program Trueorfalse;

  check:Boolean; //our Boolean variable
  sum:=0; check:=False; //preset values

  If (n > 0) and (m >0) then check := True; //first if checker

  if (sum > 20) or (n*m < sum) then check := False; //second if checker

  If check = True then writeln('Our boolean is true!') 
  else writeln('Our boolean is false!'); //final output checker



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