Evaluate/Calculate
This is submitted as two extension methods as they work together. It is based off of an class designed by sfabriz @ http://www.osix.net/modules/article/?id=761 He has another class that does something a little different but I thought this was a wonderful piece of code so encapsulated it here. I only claim authorship of the conversion and not the underlying logic.
Source
/// <summary>
/// JavaScript style Eval for simple calculations
/// http://www.osix.net/modules/article/?id=761
/// This is a safe evaluation. IE will not allow for injection.
/// </summary>
/// <param name="e"></param>
/// <returns></returns>
public static string Evaluate(this string e)
{
Func<string, bool> VerifyAllowed = e1 =>
{
string allowed = "0123456789+-*/()%.,";
for (int i = 0; i < e1.Length; i++)
{
if (allowed.IndexOf("" + e1[i]) == -1)
{
return false;
}
}
return true;
};
if (e.Length == 0) { return string.Empty; }
if (!VerifyAllowed(e)) { return "String contains illegal characters"; }
if (e[0] == '-') { e = "0" + e; }
string res = "";
try
{
res = Calculate(e).ToString();
}
catch
{
return "The call caused an exception";
}
return res;
}
/// <summary>
/// JavaScript Eval Calculations for simple calculations
/// http://www.osix.net/modules/article/?id=761
/// This is an unsafe calculation. IE may allow for injection.
/// </summary>
/// <param name="e"></param>
/// <returns></returns>
public static double Calculate(this string e)
{
e = e.Replace(".", ",");
if (e.IndexOf("(") != -1)
{
int a = e.LastIndexOf("(");
int b = e.IndexOf(")", a);
double middle = Calculate(e.Substring(a + 1, b - a - 1));
return Calculate(e.Substring(0, a) + middle.ToString() + e.Substring(b + 1));
}
double result = 0;
string[] plus = e.Split('+');
if (plus.Length > 1)
{
// there were some +
result = Calculate(plus[0]);
for (int i = 1; i < plus.Length; i++)
{
result += Calculate(plus[i]);
}
return result;
}
else
{
// no +
string[] minus = plus[0].Split('-');
if (minus.Length > 1)
{
// there were some -
result = Calculate(minus[0]);
for (int i = 1; i < minus.Length; i++)
{
result -= Calculate(minus[i]);
}
return result;
}
else
{
// no -
string[] mult = minus[0].Split('*');
if (mult.Length > 1)
{
// there were some *
result = Calculate(mult[0]);
for (int i = 1; i < mult.Length; i++)
{
result *= Calculate(mult[i]);
}
return result;
}
else
{
// no *
string[] div = mult[0].Split('/');
if (div.Length > 1)
{
// there were some /
result = Calculate(div[0]);
for (int i = 1; i < div.Length; i++)
{
result /= Calculate(div[i]);
}
return result;
}
else
{
// no /
string[] mod = mult[0].Split('%');
if (mod.Length > 1)
{
// there were some %
result = Calculate(mod[0]);
for (int i = 1; i < mod.Length; i++)
{
result %= Calculate(mod[i]);
}
return result;
}
else
{
// no %
return double.Parse(e);
}
}
}
}
}
}Example
string e = "10+10*4".Evaluate();
double d = "10+10*4".Calculate();