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  1. #include <stdio.h>
  2. #include <math.h>
  3.  
  4. typedef enum { CONSTANT, VARIABLE, OPERATOR } ExpressionType;
  5.  
  6. typedef struct {
  7. 	ExpressionType expressionType;
  8. 	void* expression;
  9. } Expression;
  10.  
  11. typedef struct {} Variable;
  12.  
  13. typedef struct {
  14. 	float value;
  15. } Constant;
  16.  
  17. typedef enum { PLUS, MINUS, MULTIPLY, DIVIDE } OperatorType;
  18.  
  19. typedef struct {
  20. 	OperatorType operatorType;
  21. 	Expression a;
  22. 	Expression b;
  23. } Operator;
  24.  
  25. typedef struct {
  26. 	Variable* variable;
  27. 	float value;
  28. } Binding;
  29.  
  30. typedef struct {
  31. 	Binding* bindings;
  32. 	size_t size;
  33. } Context;
  34.  
  35. float value(Variable* variable, Context context) {
  36. 	for (size_t i = 0; i < context.size; i++) {
  37. 		if (context.bindings[i].variable == variable) {
  38. 			return context.bindings[i].value;
  39. 		}
  40. 	}
  41.  
  42. 	return NAN;
  43. }
  44.  
  45. float result(Expression expression, Context context);
  46.  
  47. float resultOfOperator(Operator* op, Context context) {
  48. 	float aResult = result(op->a, context);
  49. 	float bResult = result(op->b, context);
  50.  
  51. 	switch (op->operatorType) {
  52. 	case PLUS:
  53. 		return aResult + bResult;
  54.  
  55. 	case MINUS:
  56. 		return aResult - bResult;
  57.  
  58. 	case MULTIPLY:
  59. 		return aResult * bResult;
  60.  
  61. 	case DIVIDE:
  62. 		return aResult / bResult;
  63. 	}
  64.  
  65. 	return NAN;
  66. }
  67.  
  68. float result(Expression expression, Context context) {
  69. 	switch (expression.expressionType) {
  70. 	case CONSTANT:
  71. 		return *(float*)expression.expression;
  72.  
  73. 	case VARIABLE:
  74. 		return value((Variable*)expression.expression, context);
  75.  
  76. 	case OPERATOR:
  77. 		return resultOfOperator((Operator*)expression.expression, context);
  78. 	}
  79.  
  80. 	return NAN;
  81. }
  82.  
  83. int main(void) {
  84. 	Variable a;
  85. 	Variable b;
  86. 	Variable c;
  87. 	Variable d;
  88.  
  89. 	Constant five = { 5.0 };
  90. 	Operator divide = { DIVIDE, { VARIABLE, &a }, { VARIABLE, &b } };
  91. 	Operator multiply = { MULTIPLY, { OPERATOR, &divide }, { VARIABLE, &c } };
  92. 	Operator minus = { MINUS, { OPERATOR, &multiply }, { VARIABLE, &d } };
  93. 	Operator plus = { PLUS, { OPERATOR, &minus }, { CONSTANT, &five } };
  94.  
  95. 	Expression expression = { OPERATOR, &plus };
  96.  
  97. 	Binding bindings[] = { { &a, 1.0 }, { &b, 2.0 }, { &c, 3.0 }, { &d, 4.0 } };
  98. 	Context context = { bindings, sizeof bindings };
  99. 	printf("%f", result(expression, context));
  100.  
  101. 	return 0;
  102. }
  103.  
Success #stdin #stdout 0s 2156KB
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https://ideone.com/RTLC6U
language:
C (gcc 8.3)
created:
10 years ago
visibility:
secret

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