false and true

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Revision as of 12:00, 4 May 2018 by Kai Burghardt (talk | contribs) (use Template:Translate; add hint about typecasting)
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The constants false and true are used to define the false and true conditions of a boolean variable. They are manifest constants that are defined as part of the standard data types the compiler initially knows about.

These constant values must be predefined by the compiler as there is no way to define them in terms of anything else.

internal value

program falseDemo(input, output, stderr);


	writeLn(false);                            // prints FALSE
	// enumerative actions ------------------------------------------
	writeLn(ord(false));                       // prints 0
	writeLn(succ(false));                      // prints TRUE
	// next two statements generate out-of-range compile-time warnings
	writeLn(pred(false));                      // prints TRUE
	writeLn(succ(succ(false)));                // prints TRUE
	// data type ----------------------------------------------------
	writeLn(sizeOf(false));                    // prints 1
	writeLn(bitSizeOf(false));                 // prints 8
	writeLn(PTypeInfo(typeInfo(false))^.kind); // prints tkBool
	writeLn(PTypeInfo(typeInfo(false))^.name); // prints Boolean

When typecasting or interpreting any numeric value as a boolean value, it is important to know, that any non-zero value means true whilst only 0 (zero) is false.