public static int Calculate(string expression)
{
int firstNumber = 0;
int i = 0;
bool isNegative = false;
if (expression[0] == '-')
{
isNegative = true;
++i;
}
while (expression[i] >= '0' && expression[i] <= '9')
{
firstNumber = firstNumber * 10 + (int)expression[i] - 48;
++i;
if (i == expression.Length)
{
if (isNegative)
{
firstNumber = 0 - firstNumber;
}
return firstNumber;
}
}
if (isNegative)
{
firstNumber = 0 - firstNumber;
}
int operationPlace = i;
++i;
int secondNumber = 0;
while (i < expression.Length)
{
secondNumber = secondNumber * 10 + (int)expression[i] - 48;
++i;
}
var calc = new StackCalculator(new Stack());
calc.Push(firstNumber);
calc.Push(secondNumber);
switch (expression[operationPlace])
{
case '/':
calc.Divide();
break;
case '*':
calc.Multiply();
break;
case '+':
calc.Add();
break;
case '-':
calc.Subtract();
break;
}
return calc.Result();
}
