fork(1) download 
  1. {$mode objfpc} {$coperators+} {$modeswitch duplicatelocals}
  2. uses
  3. 	SysUtils, StrUtils, Math;
  4.  
  5. type
  6. 	Calculator = object
  7. 		class function Calculate(const s: string): double; static;
  8.  
  9. 	private	type
  10. 		OpEnum = (NoOp, PlusOp, MinusOp, MulOp, DivOp, PowOp);
  11. 	const
  12. 		OpSyms: array[PlusOp .. High(OpEnum)] of char = '+-*/^';
  13. 		OpPrecedences: array[OpEnum] of int32 = (-1, 0, 0, 1, 1, 2);
  14. 		RightAssocOps = [PowOp];
  15. 	var
  16. 		s: string;
  17. 		p: SizeInt;
  18. 		function ScanPart(lhs: double; minPrecedence: SizeInt): double;
  19. 		function ScanPrimary: double;
  20. 		procedure SkipSpaces;
  21. 		procedure Fail(const what: string);
  22. 		function RecognizeOperator: OpEnum;
  23. 	end;
  24.  
  25. 	class function Calculator.Calculate(const s: string): double;
  26. 	var
  27. 		c: Calculator;
  28. 	begin
  29. 		c.s := s;
  30. 		c.p := 1;
  31. 		result := c.ScanPart(c.ScanPrimary, 0);
  32. 		if c.p <= length(s) then c.Fail('неожиданное продолжение');
  33. 	end;
  34.  
  35. 	function Calculator.ScanPart(lhs: double; minPrecedence: SizeInt): double;
  36. 	var
  37. 		op, nextOp: OpEnum;
  38. 		rhs: double;
  39. 	begin
  40. 		nextOp := RecognizeOperator;
  41. 		repeat
  42. 			op := nextOp;
  43. 			if OpPrecedences[op] < minPrecedence then exit(lhs);
  44. 			p += 1;
  45. 			rhs := ScanPrimary;
  46. 			nextOp := RecognizeOperator;
  47. 			while OpPrecedences[nextOp] + ord(nextOp in RightAssocOps) > OpPrecedences[op] do
  48. 			begin
  49. 				rhs := ScanPart(rhs, OpPrecedences[op] + ord(OpPrecedences[nextOp] > OpPrecedences[op]));
  50. 				nextOp := RecognizeOperator;
  51. 			end;
  52. 			case op of
  53. 				NoOp: ;
  54. 				PlusOp: lhs := lhs + rhs;
  55. 				MinusOp: lhs := lhs - rhs;
  56. 				MulOp: lhs := lhs * rhs;
  57. 				DivOp: lhs := lhs / rhs;
  58. 				PowOp: lhs := Power(lhs, rhs);
  59. 			end;
  60. 		until false;
  61. 	end;
  62.  
  63. 	function Calculator.ScanPrimary: double;
  64. 	var
  65. 		nume: SizeInt;
  66. 	begin
  67. 		SkipSpaces;
  68. 		if p > length(s) then Fail('неожиданный конец');
  69. 		if s[p] = '(' then
  70. 		begin
  71. 			p += 1;
  72. 			result := ScanPart(ScanPrimary(), 0);
  73. 			if (p > length(s)) or (s[p] <> ')') then Fail('ожидается )');
  74. 			p += 1;
  75. 			exit;
  76. 		end;
  77. 		nume := p;
  78. 		while (nume <= length(s)) and ((s[nume] in ['0' .. '9', '.']) or (nume = p) and (s[nume] in ['-', '+'])) do nume += 1;
  79. 		if TryStrToFloat(Copy(s, p, nume - p), result) then
  80. 		begin
  81. 			p := nume;
  82. 			exit;
  83. 		end;
  84. 		case s[p] of
  85. 			'+': begin p += 1; exit(ScanPrimary()); end;
  86. 			'-': begin p += 1; exit(-ScanPrimary()); end;
  87. 			else Fail('ожидается число, унарный оператор, или скобка');
  88. 		end;
  89. 	end;
  90.  
  91. 	procedure Calculator.SkipSpaces;
  92. 	begin
  93. 		while (p <= length(s)) and (s[p] = ' ') do p += 1;
  94. 	end;
  95.  
  96. 	procedure Calculator.Fail(const what: string);
  97. 	begin
  98. 		raise Exception.Create(StuffString(s, p, 0, '|') + ': ' + what + '.');
  99. 	end;
  100.  
  101. 	function Calculator.RecognizeOperator: OpEnum;
  102. 	begin
  103. 		SkipSpaces;
  104. 		if p <= length(s) then
  105. 			for result := PlusOp to High(OpEnum) do
  106. 				if OpSyms[result] = s[p] then exit;
  107. 		result := NoOp;
  108. 	end;
  109.  
  110. const
  111. 	Examples: array[0 .. 2] of string =
  112. 	(
  113. 		'2 + 2 * 2',
  114. 		'(2 + --3) * 2^2^(1 + 1)^2',
  115. 		'2^^^2'
  116. 	);
  117.  
  118. var
  119. 	ex: string;
  120.  
  121. begin
  122. 	for ex in Examples do
  123. 		try
  124. 			writeln(ex + ' = ' + FloatToStr(Calculator.Calculate(ex)));
  125. 		except
  126. 			on e: Exception do writeln(e.Message);
  127. 		end;
  128. end.
Success #stdin #stdout 0.01s 5304KB
comments (?)
stdin 
Standard input is empty
stdout 
2 + 2 * 2 = 6
(2 + --3) * 2^2^(1 + 1)^2 = 327680
2^|^^2: ожидается число, унарный оператор, или скобка.
https://ideone.com/lEIunA
language:
Pascal (fpc 3.0.4)
created:
1 year ago
visibility:
secret

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