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  1. #include<bits/stdc++.h>
  2.  
  3. //Evaluating infix expression without converting it into postfix in a single scan
  4.  
  5. int isoperand(char x)
  6. {
  7. 	if(x == '+' || x=='-'|| x=='*' || x=='/' || x==')' || x=='(')
  8. 		return 0;
  9. 	return 1;
  10. }
  11.  
  12. int Pre(char x)
  13. {
  14. 	if(x == '+' || x == '-')
  15. 		return 1;
  16. 	if(x == '*' || x == '/')
  17. 		return 3;
  18. 	return 0;
  19. }
  20.  
  21. int postfixevaluation(std::string exp)
  22. {
  23. 	std::stack<int> operandStack;
  24. 	std::stack<char> operatorStack;
  25. 	int i,x,y,z,operand;
  26. 	i=0;
  27. 	while(exp[i]!='\0')
  28. 	{
  29. 		if(exp[i]==' ' || exp[i]==',')
  30. 		{
  31. 			i++;
  32. 			continue;
  33. 		}
  34.  
  35. 		if(isoperand(exp[i]))
  36. 		{
  37. 			operand = 0;
  38. 			while(i<exp.length() && isoperand(exp[i]))
  39. 				operand = operand*10 + (exp[i++]-'0');
  40. 			operandStack.push(operand);
  41.  
  42. 		}
  43. 		else if(!isoperand(exp[i]) && operatorStack.empty())
  44. 			operatorStack.push(exp[i++]);
  45. 		else if(!isoperand(exp[i]) && !operatorStack.empty())
  46. 		{
  47. 			if(exp[i]=='(')
  48. 				operatorStack.push(exp[i++]);
  49. 			else if(Pre(exp[i])>Pre(operatorStack.top()) && exp[i]!=')')
  50. 				operatorStack.push(exp[i++]);
  51. 			else if(exp[i]==')' && operatorStack.top() == '(')
  52. 			{
  53. 				operatorStack.pop();
  54. 				i++;
  55. 			}
  56.  
  57. 			else
  58. 			{
  59. 				x = operandStack.top();
  60. 				operandStack.pop();
  61. 				y = operatorStack.top();
  62. 				operatorStack.pop();
  63. 				z = operandStack.top();
  64. 				operandStack.pop();
  65. 				if(y == '+')
  66. 					operandStack.push(z+x);
  67. 				else if(y == '-')
  68. 					operandStack.push(z-x);
  69. 				else if(y == '*')
  70. 					operandStack.push(x*z);
  71. 				else if(y == '/')
  72. 					operandStack.push(z/x);
  73. 			} 
  74. 		}
  75. 	}
  76. 	while(!operatorStack.empty())
  77. 	{
  78. 		x = operandStack.top();
  79. 		operandStack.pop();
  80. 		y = operatorStack.top();
  81. 		operatorStack.pop();
  82. 		z = operandStack.top();
  83. 		operandStack.pop();
  84. 		if(y == '+')
  85. 			operandStack.push(x+z);
  86. 		else if(y == '-')
  87. 			operandStack.push(z-x);
  88. 		else if(y == '*')
  89. 			operandStack.push(x*z);
  90. 		else if(y == '/')
  91. 			operandStack.push(z/x);
  92. 	}
  93. 	return operandStack.top();
  94. }
  95.  
  96. int main(int argc, char const *argv[])
  97. {
  98. 	std::string s;
  99. 	getline(std::cin,s);
  100. 	std::cout<<postfixevaluation(s)<<std::endl;
  101. 	return 0;
  102. }
  103.  
Success #stdin #stdout 0s 4288KB
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stdin
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3-5*10/5+10
stdout
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3
https://ideone.com/IV8PAU
language:
C++ (gcc 8.3)
created:
6 years ago
visibility:
public

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