StringToFormula

Parses a C# string representing an expression, an equality/inequality, or a Boolean term and returns a numeric value.

How to Use

The entire parser is in a single class so you can add just 1 file to your project and you're able to parse any string input and return a double value. No need to include an external DLL if you're trying to create small executible without external dependecies.

string input = "1 + 2 / 3 - 5 * 2.5";

var parser = new StringToFormula();
double output = parser.Eval(input);    // expected -10.8333

Coverage

This parser will handle:

• Simple mathmetical expressions including PEMDAS (paranthesis, exponents, multiplication, division, addition, and subtraction)
  • The order of evaluation is always PEMDAS and then left-to-right
• Equalities including:
  • == : equals
  • != : not equals
  • <= : less than or equal to
  • >= : greater than or equal to
  • < : less than
  • > : greater than
• Boolean AND and OR operators
  • &: default AND (customizable)
  • |: default OR (customizable)
• Negation operator ! will convert any 0 to 1 and any non-zero to 0

Sample Passing Code

Expressions

• (1) + (2) = 3
• (1--1)^1.52 = 2.86791
• (2+-2^0.2)/10*5+(1--1)^1.52 = 3.293561
• (2+-2^0.2)/10*5+(1--1)^1.52*-2 = -5.310
• (-1 * -4) = 4
• 1/2+3 = 3.5
• -1 --1 = 0
• +1 --1 = 2
• (-1 * 4) = -4
• -1 * 4 = -4
• bad input = double.NaN
• 1/0 = double.PositiveInfinity
• -1/0 = double.NegativeInfinity
• 1 * -4 = -4
• -1 * -4 = 4
• 2^3 = 8
• -2^3 = -8
• 2^-2 = 0.25
• -2^2 = 4
• -4 / -2 = 2
• -4 / 2 = -2
• 4 / -2 = -2
• 2+-2 = 0
• (2+-2) = 0
• (12 / 12 * (10 + 10)) / 2 = 10
• (12 / 12.5 * (10 + 10)) / 2.1 = 9.142857
• (2 + -2) / 10 * 5 + (1 - -1) * -2 = -4
• (2+-2)/10*5+(1--1)^12*-2 = -8192

Equalities

• 1 == 1 = 1
• 1 == 2 = 0
• 1 < 2 = 1
• 1<=1 = 1
• 1 != 2 = 1
• 1 > 2 = 0
• 1>=1 = 1
• 2 != 1 = 1

Boolean

• 1 * 0 & 1 = 0
• 1 & 0 = 0
• 1 & 1 = 1
• 0 & 0 = 1
• 1 & 0 & 1 & 0 = 0
• 1 & 0 & 0 | 0 = 0
• 1 & 0 & 0 | 1 = 1
• 1 & 0 & 0 | 0 | 1 = 1
• 2 & 0 | 2 = 1
• 1 | 1 & 0 | 0 = 1
• (1 | 0) & (0 | 1) = 1
• (1 | 0) | (0 & 1) = 1
• (1 | 0) & (0 & 0) = 1
• (1 | 0) & (1 & 0) = 0
• (1 | 0) | (1 & 0) = 1
• 1 + 2 & 3 + 4 = 1
• 0 / 1 | 1 / 1 = 1

Negation

• !1 + 2 = 2
• !0 + !0 + !0 = 3
• !1 = 0
• !0 = 1
• !(1) = 0
• !(!(0 / 1)) = 0
• !!1 = 0
• !!0 = 1

Custom Settings

You can customize the boolean AND and OR operators. By default, these are & and | respectively, but some languages use && and || as the operators. To change these default values, simply access the GetSettings() method and update the operator:

string input = "(1 || 0) && (1)";

var parser = new StringToFormula();

var ps = parser.GetSettings();
ps.AndString = "&&";
ps.OrString = "||";

double output = parser.Eval(input);   // expected 1