uCalc API Version: 5.7.0-preview.1 Released: 7/30/2026

Warning

uCalc API Preview Release Notice:This preview documentation describes the intended behavior of the API. It is not fully accurate or complete.The current preview build contains incomplete features, unoptimized performance, and is subject to breaking changes.Use of the preview version in your production code is not recommended.

Eval

Method

Product: 

Fast Math Parser

Class: 

uCalc

Parses and evaluates a string expression in a single step, returning a numeric result.

Syntax

Eval(string)

Parameters

expression
string
The string containing the mathematical, or logical expression to parse and evaluate.

Return

double

The double-precision floating-point result of the evaluated expression.

Remarks

The Eval method provides a convenient one-step shortcut to parse and immediately evaluate an expression, returning its result. It is ideal for scenarios where an expression is evaluated only once and performance is not the primary concern.

When to Use Eval

Eval is the simplest way to get a result from a string. However, it performs two operations internally: parsing and evaluation. If you need to evaluate the same expression multiple times (e.g., in a loop), it is significantly more efficient to use the two-step approach:

  1. Call uCalc.Parse once to create a compiled Expression object.
  2. Call Expression.Evaluate repeatedly on that object.

This avoids the overhead of re-parsing the string on every iteration.

⚠️ Return Type Limitation

This function is specifically designed for expressions that yield a simple numeric result. It always returns a double.

  • If the expression's natural result is another numeric type (like Int32 or Boolean), the value will be converted to a double.
  • If the expression yields a non-numeric or complex type (like a String or Complex number), the return value will be meaningless. No error is raised in this case.

For expressions that return non-numeric types or to get a string representation of any result, use the more versatile uCalc.EvalStr method instead.

Supported Syntax

The expression string can contain any combination of numbers, variables, and calls to built-in or user-defined Functions and Operators.

Comparative Analysis

  • vs. C# DataTable.Compute: A common workaround in .NET for evaluating strings is using the Compute method of a DataTable. While it works for simple arithmetic, it is far less powerful, significantly slower, and lacks the rich feature set of uCalc (custom functions, complex numbers, transformers, etc.).
  • vs. Other Parsing Libraries (e.g., NCalc, Flee): Many libraries offer similar Evaluate() methods. uCalc's Eval differentiates itself by being part of a much larger, cohesive engine. The expression can leverage custom data types, operators, and transformation rules defined within the same uCalc instance, offering greater flexibility and power than single-purpose evaluation libraries.
  • vs. Parse + Evaluate: As mentioned, Eval is for convenience. The two-step process is for performance-critical applications.

Examples

Quickly evaluates several basic mathematical and function-based expressions.

ID: 334

See: Eval 
				
					using uCalcSoftware;

var uc = new uCalc();
// Eval provides a direct way to compute results from strings.
Console.WriteLine(uc.Eval("1+1"));
Console.WriteLine(uc.Eval("5*(3+9)^2"));
Console.WriteLine(uc.Eval("Sqrt(16) + Sin(0)"));
Console.WriteLine(uc.Eval("Length('This is a test')"));
				
			
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   // Eval provides a direct way to compute results from strings.
   cout << uc.Eval("1+1") << endl;
   cout << uc.Eval("5*(3+9)^2") << endl;
   cout << uc.Eval("Sqrt(16) + Sin(0)") << endl;
   cout << uc.Eval("Length('This is a test')") << endl;
}
				
			
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720
4
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					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      '// Eval provides a direct way to compute results from strings.
      Console.WriteLine(uc.Eval("1+1"))
      Console.WriteLine(uc.Eval("5*(3+9)^2"))
      Console.WriteLine(uc.Eval("Sqrt(16) + Sin(0)"))
      Console.WriteLine(uc.Eval("Length('This is a test')"))
   End Sub
End Module
				
			
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720
4
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Calculates simple interest by defining variables and then evaluating an expression string that uses them.

ID: 335

See: Eval 
				
					using uCalcSoftware;

var uc = new uCalc();
// Define variables representing configuration or user inputs.
uc.DefineVariable("principal = 20000");
uc.DefineVariable("annual_rate = 0.0575");
uc.DefineVariable("years = 4");

// Evaluate an expression combining these variables.
var interest = uc.Eval("principal * annual_rate * years");
Console.WriteLine($"Total Interest: {interest}");
				
			
Total Interest: 4600
Explore 600+ other examples
				
					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   // Define variables representing configuration or user inputs.
   uc.DefineVariable("principal = 20000");
   uc.DefineVariable("annual_rate = 0.0575");
   uc.DefineVariable("years = 4");

   // Evaluate an expression combining these variables.
   auto interest = uc.Eval("principal * annual_rate * years");
   cout << "Total Interest: " << interest << endl;
}
				
			
Total Interest: 4600
Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      '// Define variables representing configuration or user inputs.
      uc.DefineVariable("principal = 20000")
      uc.DefineVariable("annual_rate = 0.0575")
      uc.DefineVariable("years = 4")
      
      '// Evaluate an expression combining these variables.
      Dim interest = uc.Eval("principal * annual_rate * years")
      Console.WriteLine($"Total Interest: {interest}")
   End Sub
End Module
				
			
Total Interest: 4600
Explore 600+ other examples
Evaluating expressions

ID: 21

See: (Constructor), Eval, EvalB, EvalStrB 
				
					using uCalcSoftware;

var uc = new uCalc();
// See EvalStr for more examples.

Console.WriteLine(uc.Eval("1+1"));
Console.WriteLine(uc.Eval("5*(3+9)^2"));
Console.WriteLine(uc.Eval("Length('This is a test')"));
				
			
2
720
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   // See EvalStr for more examples.

   cout << uc.Eval("1+1") << endl;
   cout << uc.Eval("5*(3+9)^2") << endl;
   cout << uc.Eval("Length('This is a test')") << endl;
}
				
			
2
720
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Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      '// See EvalStr for more examples.
      
      Console.WriteLine(uc.Eval("1+1"))
      Console.WriteLine(uc.Eval("5*(3+9)^2"))
      Console.WriteLine(uc.Eval("Length('This is a test')"))
   End Sub
End Module
				
			
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720
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A minimal example defining a function inline to calculate the area of a rectangle.

ID: 296

See: DefineFunction, DefineVariable, Eval 
				
					using uCalcSoftware;

var uc = new uCalc();
uc.DefineVariable("x = 5");
uc.DefineFunction("Area(length, width) = length * width");
Console.WriteLine(uc.Eval("Area(4, x) + 7"));
				
			
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   uc.DefineVariable("x = 5");
   uc.DefineFunction("Area(length, width) = length * width");
   cout << uc.Eval("Area(4, x) + 7") << endl;
}
				
			
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					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      uc.DefineVariable("x = 5")
      uc.DefineFunction("Area(length, width) = length * width")
      Console.WriteLine(uc.Eval("Area(4, x) + 7"))
   End Sub
End Module
				
			
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A quick start example showing defining a variable, a function, and evaluating an expression.

ID: 1296

See: DefineFunction, DefineVariable, Eval, Introduction 
				
					using uCalcSoftware;

var uc = new uCalc();
uc.DefineVariable("x = 10");
uc.DefineFunction("DoubleThis(n) = n * 2");

Console.WriteLine(uc.Eval("DoubleThis(x) + 5"));
				
			
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   uc.DefineVariable("x = 10");
   uc.DefineFunction("DoubleThis(n) = n * 2");

   cout << uc.Eval("DoubleThis(x) + 5") << endl;
}
				
			
25
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					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      uc.DefineVariable("x = 10")
      uc.DefineFunction("DoubleThis(n) = n * 2")
      
      Console.WriteLine(uc.Eval("DoubleThis(x) + 5"))
   End Sub
End Module
				
			
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Demonstrates defining a function that is implemented by a native callback in the host application.

ID: 297

See: Arg, DefineFunction, Eval, Return 
				
					using uCalcSoftware;

var uc = new uCalc();

static void MyAreaCallback(uCalc.Callback cb) {
   var length = cb.Arg(1);
   var width = cb.Arg(2);
   cb.Return(length * width);
}


// The signature is defined, but the logic is provided by 'MyAreaCallback'.
uc.DefineFunction("Area(x, y)", MyAreaCallback);
Console.WriteLine(uc.Eval("Area(3, 4)"));
				
			
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

void ucalc_call MyAreaCallback(uCalcBase::Callback cb) {
   auto length = cb.Arg(1);
   auto width = cb.Arg(2);
   cb.Return(length * width);
}

int main() {
   uCalc uc;
   // The signature is defined, but the logic is provided by 'MyAreaCallback'.
   uc.DefineFunction("Area(x, y)", MyAreaCallback);
   cout << uc.Eval("Area(3, 4)") << endl;
}
				
			
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					Imports System
Imports uCalcSoftware
Public Module Program
   
   Public Sub MyAreaCallback(ByVal cb As uCalc.Callback)
      Dim length = cb.Arg(1)
      Dim width = cb.Arg(2)
      cb.Return(length * width)
   End Sub
   
   Public Sub Main()
      Dim uc As New uCalc()
      '// The signature is defined, but the logic is provided by 'MyAreaCallback'.
      uc.DefineFunction("Area(x, y)", AddressOf MyAreaCallback)
      Console.WriteLine(uc.Eval("Area(3, 4)"))
   End Sub
End Module
				
			
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