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using System;
using System.Linq;
using System.Collections.Generic;
using System.Text;
namespace ExpressionEvaluator
{
class Program
{
static void Main(string[] args)
{
// 2 + 3 infix
// + 2 3 prefix
// 2 3 + postfix
var expression = "2+2^10"; // 10
var result = Evaluate(expression);
Console.WriteLine(result);
}
static double Evaluate(string expression)
{
var allowedOperators = "+-/*^";
var numbers = new Stack<double>();
var operators = new Stack<char>();
for (int i = 0; i < expression.Length; i++)
{
var @char = expression[i];
if (@char == '(')
{
operators.Push(@char);
}
else if (@char == ')')
{
while (operators.Peek() != '(')
{
var op = operators.Pop();
var param2 = numbers.Pop();
var param1 = numbers.Pop();
var newValue = ApplyOperation(op, param1, param2);
numbers.Push(newValue);
}
operators.Pop(); // (
}
else if (allowedOperators.Contains(@char))
{
while(operators.Count > 0 && Priority(operators.Peek()) >= Priority(@char))
{
var op = operators.Pop();
var param2 = numbers.Pop();
var param1 = numbers.Pop();
var newValue = ApplyOperation(op, param1, param2);
numbers.Push(newValue);
}
operators.Push(@char);
}
else if (char.IsDigit(@char) || @char == '.')
{
var number = new StringBuilder();
while (char.IsDigit(@char) || @char == '.')
{
number.Append(@char);
i++;
if (i == expression.Length)
{
break;
}
@char = expression[i];
}
i--;
numbers.Push(double.Parse(number.ToString()));
}
}
while (operators.Count > 0)
{
var op = operators.Pop();
var param2 = numbers.Pop();
var param1 = numbers.Pop();
var newValue = ApplyOperation(op, param1, param2);
numbers.Push(newValue);
}
return numbers.Pop();
}
static double ApplyOperation(char operation, double operand1, double operand2)
{
switch (operation)
{
case '+': return operand1 + operand2;
case '-': return operand1 - operand2;
case '*': return operand1 * operand2;
case '/': return operand1 / operand2;
case '^': return Math.Pow(operand1, operand2);
default: return 0.0;
}
}
static int Priority(char operation)
{
switch (operation)
{
case '+': return 1;
case '-': return 1;
case '*': return 2;
case '/': return 2;
case '^': return 3;
default: return 0;
}
}
}
}
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