Minus

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-

The symbol - (pronounced “minus”) is used to

• indicate the negative sign of a number
• subtract two numbers (using infix notation)
• form the difference of two sets.

program minusDemo(input, output, stderr);

var
	x: longint;
	g: longint;
	m: set of (foo, bar);

begin
	// unary operator: negative sign
	x := -42;                     // x becomes negative 42
	
	// binary operator: difference of numbers
	g := 144 - 169;               // g becomes negative 25
	
	// binary operator: difference of sets
	m := [foo, bar] - [bar];      // m becomes {foo}
end.

Beware: The result's target of subtractions should be a signed integer. If it's not, with {$rangechecks}} enabled, it will cause an Run-time error. Otherwise an arithmetically wrong result is produced.

program faultySubtraction(input, output, stderr);

var
	x, y: longword;

begin
	y := 1;
	{$push}
	{$rangechecks off} // otherwise the next expression
	x := 0 - y;        // yields RTE 201
	{$pop}
	
	writeLn(x);
end.

This program prints 4294967295, which equals to high(longword) because of the (unsigned) integer overflow.