Practical NCalc Examples: Parsing, Evaluating, and Debugging

How to Use NCalc for Dynamic Calculations and Formulas

What NCalc is

NCalc is a lightweight .NET expression-evaluator that parses and evaluates mathematical and logical expressions from strings. It supports parameters (static, expression-based, and dynamic), custom functions, caching, lambda compilation, async functions (via a separate package), and JSON serialization of parsed expressions.

Quick start (basic usage)

csharp
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using NCalc;

// evaluate a simple expression
var expr = new Expression(“2 + 35”);
var result = expr.Evaluate(); // 17

Parameters (static, expression, dynamic)

• Static:

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var e = new Expression(“2 * [x] + [y]”);
e.Parameters[“x”] = 5;
e.Parameters[“y”] = 1;
e.Evaluate();

• Expression parameters:

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var vol = new Expression(”[surface] * h”);
var surface = new Expression(”[l] * [L]”);
vol.Parameters[“surface”] = surface;
surface.Parameters[“l”] = 1;
surface.Parameters[“L”] = 2;
vol.Evaluate();

• Dynamic parameters:

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var e = new Expression(“Round(Pow([Pi],2) + [X], 2)”);
e.DynamicParameters[“Pi”] = _ => 3.14159;
e.Parameters[“X”] = 10;
e.Evaluate();

Custom functions

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var e = new Expression(“Secret(3,6)”);
e.EvaluateFunction += (name, args) => {
  if (name == “Secret”)
    args.Result = (int)args.Parameters[0].Evaluate() + (int)args.Parameters[1].Evaluate();
};
e.Evaluate(); // 9

Advanced features

• Lambda compilation (NCalc.LambdaCompilation) to convert expressions to delegates:

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var expr = new Expression(“1 + 2”);
Func<int> fn = expr.ToLambda<int>();
fn(); // 3

• Async support via NCalcAsync package for async functions/parameters.
• Caching: NCalc caches parsed expressions; you can control caching via options or plugins.
• JSON serialization (on .NET 8+) for parsed LogicalExpression objects.

Common options and patterns

• Use square brackets or curly braces for parameter names with special chars: [My Param] or {MyParam}.
• Use ExpressionOptions (e.g., NoCache, IgnoreCase, AllowNullParameter, IterateParameters).
• For repeated evaluations, predefine Parameters or compile to a lambda to improve performance.

Error handling and debugging

• Wrap Evaluate() in try/catch to capture parse/evaluation exceptions.
• For complex expressions, break into sub-expressions using Expression parameters to simplify debugging.
• Use EvaluateFunction/EvaluateParameter events to inspect/runtime-resolve values.

When to precompile

Precompile (ToLambda) or cache when the same parsed expression will be evaluated many times — compilation has upfront cost but greatly reduces per-evaluation time.

Useful links

• Official repo & docs: https://github.com/ncalc/ncalc and https://ncalc.github.io/ncalc

If you want, I can provide a small runnable sample project demonstrating dynamic parameters + custom functions and lambda compilation.