Difference between revisions of "Basic Pascal Tutorial/Chapter 1/Variables and Data Types"
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Variables are similar to constants, but their values can be changed as the program runs. Variables must first be declared in Pascal before they can be used: | Variables are similar to constants, but their values can be changed as the program runs. Variables must first be declared in Pascal before they can be used: | ||
| − | + | <delphi> | |
| − | + | var | |
| − | + | IdentifierList1 : DataType1; | |
| − | + | IdentifierList2 : DataType2; | |
| − | + | IdentifierList3 : DataType3; | |
| − | + | ... | |
| + | </delphi> | ||
<tt>IdentifierList</tt> is a series of identifiers, separated by commas (<tt>,</tt>). All identifiers in the list are declared as being of the same data type. | <tt>IdentifierList</tt> is a series of identifiers, separated by commas (<tt>,</tt>). All identifiers in the list are declared as being of the same data type. | ||
| Line 27: | Line 28: | ||
An example of declaring several variables is: | An example of declaring several variables is: | ||
| − | + | <delphi> | |
| − | + | var | |
| − | + | age, year, grade : integer; | |
| − | + | circumference : real; | |
| − | + | LetterGrade : char; | |
| + | DidYouFail : Boolean; | ||
| + | </delphi> | ||
{|style=color-backgroud="white" cellspacing="20" | {|style=color-backgroud="white" cellspacing="20" | ||
Revision as of 15:45, 5 January 2010
1D - Variables and Data Types (author: Tao Yue, state: unchanged)
Variables are similar to constants, but their values can be changed as the program runs. Variables must first be declared in Pascal before they can be used: <delphi> var
IdentifierList1 : DataType1; IdentifierList2 : DataType2; IdentifierList3 : DataType3; ...
</delphi> IdentifierList is a series of identifiers, separated by commas (,). All identifiers in the list are declared as being of the same data type.
The basic data types in Pascal include:
- integer
- real
- char
- boolean
Standard Pascal does not make provision for the string data type, but most modern compilers do. Experienced Pascal programmers also use pointers for dynamic memory allocation, objects for object-oriented programming, and many others, but this gets you started.
More information on Pascal data types:
- The integer data type can contain integers from -32768 to 32767. This is the signed range that can be stored in a 16-bit word, and is a legacy of the era when 16-bit CPUs were common. For backward compatibility purposes, a 32-bit signed integer is a longint and can hold a much greater range of values.
- The real data type has a range from 3.4x10-38 to 3.4x1038, in addition to the same range on the negative side. Real values are stored inside the computer similarly to scientific notation, with a mantissa and exponent, with some complications. In Pascal, you can express real values in your code in either fixed-point notation or in scientific notation, with the character E separating the mantissa from the exponent. Thus, 452.13 is the same as 4.5213e2
- The char data type holds characters. Be sure to enclose them in single quotes, like so: 'a' 'B' '+' Standard Pascal uses 8-bit characters, not 16-bits, so Unicode, which is used to represent all the world's language sets in one UNIfied CODE system, is not supported.
- The boolean data type can have only two values: TRUE and FALSE
An example of declaring several variables is: <delphi> var
age, year, grade : integer; circumference : real; LetterGrade : char; DidYouFail : Boolean;
</delphi>
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