# Differences

This shows you the differences between two versions of the page.

 — lynplexs:tutorial:constants [2014/05/25 16:52] (current) Line 1: Line 1: + ====== Constants ====== + Constants can be provided within a program in two ways.  They can either be literal values or named constants. + + ===== Named Constants ===== + The best example of a named constant always seems to be //​PI//​. ​ It is a constant value although, because it has a large, possibly infinite number of decimal places, it is usually limited to only a few of those. ​ //PI// can be variously defined as 3.142, 3.14159265 or to a value with even greater accuracy. ​ It can even be defined as 22/7 for simple calculations. ​ However we define it //PI// itself is still a constant value. + + In the LynPlex interpreter constants are defined as: + const PI = 3.14159265 + ​ + //**Note:** In LynPlexS this would be defined as:// + + \$\$pi = 3.14159265 + + //and in LynPlexC as:// + + const PI [as datatype] = 3.14159265 + ​ + Assigning a name to a constant value means that you do not have to remember what the actual value is.  For example: + c = 2 * PI * r + ​ + + ===== Constants in Expressions ===== + Constants may be used anywhere in an expression. ​ For example. + put "The value of PI is" PI + will show: + The value of PI is 3.14159265 + + ===== Changing Constants ===== + Although constants are intended to remain the same throughout the program, the primary purpose of defining a value as a constant is to stop it being accidentally modified. + + Having defined //PI// as shown above, the statement: + PI = 123456 + will be rejected. + + If you really want to, you can change any constant value provided that you redefine it as a constant. ​ For example, if you want PI to have a lower precision enter: ​ + const PI = 3.142 + or + const PI = 22/7 + + ===== Page Links ===== + + |< 100% 35% - 28% - 35% >| + | <= [[literals]] ​ ^ |  [[start]] ​ ^ |  [[variables]] => |