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.

Evaluate

Method

Product: 

Fast Math Parser

Class: 

Expression

Evaluates a pre-parsed expression, returning a numeric result. This is the high-performance second step in the parse-evaluate workflow.

Syntax

Evaluate()

Parameters

[None]

Return

double

The double-precision numeric result of the evaluated expression.

Remarks

🚀 High-Performance Evaluation

The Evaluate method is the high-performance second step in uCalc's two-stage evaluation process. It executes a pre-compiled Expression object, making it exceptionally fast for repeated calculations.

The Parse-Once, Evaluate-Many Pattern

For optimal performance, especially in loops or performance-critical scenarios, you should always follow this pattern:

  1. Parse Once: Call uCalc.Parse() outside your loop to convert the string expression into a compiled, reusable Expression object.
  2. Evaluate Many: Call .Evaluate() on that object inside your loop.

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

csharp
var uc = new uCalc();
// Define the variable to be used in the expression.
var variableX = uc.DefineVariable("x");

// 1. Parse the expression once, outside the loop.
var parsedExpr = uc.Parse("x * 2");
// or var parsedExr = new uCalc.Expression(uc, "x * 2");

// 2. Evaluate it many times inside the loop with changing variables.
for (var i = 1; i <= 5; i++) {
VariableX.Value(i);
Console.WriteLine(parsedExpr.Evaluate()); // Extremely fast
}

⚙️ Data Type Handling

This method is optimized for numeric results and always returns a double. It intelligently handles various input types:

  • If the expression's result is a double, it is returned directly.
  • If the result is another numeric type (e.g., Int32, Single, Boolean), it is automatically and safely converted to a double.
  • If the expression returns a non-numeric type (like a String or Complex number), the return value will be meaningless. For these cases, use EvaluateStr() instead.

🆚 Comparative Analysis: Choosing the Right Evaluation Method

uCalc provides several ways to evaluate expressions. Choose the one that best fits your use case.

MethodReturn TypeUse CasePerformance
Expression.EvaluateDbl()doubleBest for loops. High-speed numeric calculations on a pre-parsed expression.⭐⭐⭐⭐⭐
Expression.Evaluate()doubleBest for loops. High-speed numeric calculations on a pre-parsed expression. (may convert from another numeric type to Double)⭐⭐⭐⭐
Expression.EvaluateStr()stringHigh-speed evaluation for any data type (including strings) on a pre-parsed expression.⭐⭐⭐
uCalc.Eval()doubleConvenience. One-off numeric calculations where the expression is not reused.⭐⭐
uCalc.EvalStr()stringConvenience. One-off calculations for any data type, especially for displaying user output.⭐

Why uCalc?

In many environments, evaluating expressions in a loop requires sub-optimal solutions.

  • Native Code (e.g., DataTable.Compute in .NET): These solutions are often slow, lack features (like custom functions), and re-parse the expression on every call, making them unsuitable for performance-critical loops.
  • Interpreted Languages (e.g., Python eval): While flexible, these also parse on each call and carry the overhead of a full scripting engine.

uCalc's Parse + Evaluate model provides the best of both worlds: the flexibility of runtime expressions combined with performance that approaches compiled code, because the expensive parsing work is done only once.

Examples

A simple demonstration of parsing an expression once and then evaluating it.

ID: 573

See: Evaluate 
				
					using uCalcSoftware;

var uc = new uCalc();
// 1. Parse the expression into a reusable object.
var parsedExpr = uc.Parse("100 / 4");

// 2. Evaluate the pre-parsed object.
Console.WriteLine($"Result: {parsedExpr.Evaluate()}");
				
			
Result: 25
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   // 1. Parse the expression into a reusable object.
   auto parsedExpr = uc.Parse("100 / 4");

   // 2. Evaluate the pre-parsed object.
   cout << "Result: " << parsedExpr.Evaluate() << endl;
}
				
			
Result: 25
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					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      '// 1. Parse the expression into a reusable object.
      Dim parsedExpr = uc.Parse("100 / 4")
      
      '// 2. Evaluate the pre-parsed object.
      Console.WriteLine($"Result: {parsedExpr.Evaluate()}")
   End Sub
End Module
				
			
Result: 25
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Using the parse-evaluate pattern for high-performance calculations in a loop with a changing variable.

ID: 574

See: Evaluate, uCalc SDK 
				
					using uCalcSoftware;

var uc = new uCalc();
// Define a variable 'x' that will be updated in the loop.
var variableX = uc.DefineVariable("x");

// Parse the expression just once before the loop begins.
var parsedExpr = uc.Parse("x^2 * 10");

Console.WriteLine("Evaluating 'x^2 * 10' for x = 1 to 5:");
for (double x = 1; x <= 5; x++) {
   variableX.Value(x);
   // Evaluate is very fast as the parsing work is already done.
   Console.WriteLine($"x = {x}, Result = {parsedExpr.Evaluate()}");
}
				
			
Evaluating 'x^2 * 10' for x = 1 to 5:
x = 1, Result = 10
x = 2, Result = 40
x = 3, Result = 90
x = 4, Result = 160
x = 5, Result = 250
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   // Define a variable 'x' that will be updated in the loop.
   auto variableX = uc.DefineVariable("x");

   // Parse the expression just once before the loop begins.
   auto parsedExpr = uc.Parse("x^2 * 10");

   cout << "Evaluating 'x^2 * 10' for x = 1 to 5:" << endl;
   for (double x = 1; x <= 5; x++) {
      variableX.Value(x);
      // Evaluate is very fast as the parsing work is already done.
      cout << "x = " << x << ", Result = " << parsedExpr.Evaluate() << endl;
   }
}
				
			
Evaluating 'x^2 * 10' for x = 1 to 5:
x = 1, Result = 10
x = 2, Result = 40
x = 3, Result = 90
x = 4, Result = 160
x = 5, Result = 250
Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      '// Define a variable 'x' that will be updated in the loop.
      Dim variableX = uc.DefineVariable("x")
      
      '// Parse the expression just once before the loop begins.
      Dim parsedExpr = uc.Parse("x^2 * 10")
      
      Console.WriteLine("Evaluating 'x^2 * 10' for x = 1 to 5:")
      For x  As Double = 1 To 5
         variableX.Value(x)
         '// Evaluate is very fast as the parsing work is already done.
         Console.WriteLine($"x = {x}, Result = {parsedExpr.Evaluate()}")
      Next
   End Sub
End Module
				
			
Evaluating 'x^2 * 10' for x = 1 to 5:
x = 1, Result = 10
x = 2, Result = 40
x = 3, Result = 90
x = 4, Result = 160
x = 5, Result = 250
Explore 600+ other examples
Using the parse-evaluate pattern for high-performance calculations in a loop with a changing variable w/ stopwatch.

ID: 1460

See: DefineVariable, Evaluate, Optimizing Performance in Loops, Parse, Value(double) 
				
					using uCalcSoftware;

var uc = new uCalc();
var variableX = uc.DefineVariable("x");
var userExpression = "x * 2 + 5";
var Total = 0.0;
var UpperBound = 1000000; // One million

// Parse the expression just once before the loop begins.
var parsedExpr = uc.Parse(userExpression);

var stopwatch = System.Diagnostics.Stopwatch.StartNew();
for (double x = 1; x <= UpperBound; x++) {
   variableX.Value(x);
   Total = Total + parsedExpr.Evaluate();
}
stopwatch.Stop();
//Uncomment the following line to reveal the actual speed:
//Console.WriteLine($"Elapsed Milliseconds: {stopwatch.ElapsedMilliseconds} ms");

Console.Write("Sum(1, "); Console.Write(UpperBound); Console.Write(", "); Console.Write(userExpression); Console.Write(") = "); Console.Write(Total);
				
			
Sum(1, 1000000, x * 2 + 5) = 1000006000000
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   auto variableX = uc.DefineVariable("x");
   auto userExpression = "x * 2 + 5";
   auto Total = 0.0;
   auto UpperBound = 1000000; // One million

   // Parse the expression just once before the loop begins.
   auto parsedExpr = uc.Parse(userExpression);


   for (double x = 1; x <= UpperBound; x++) {
      variableX.Value(x);
      Total = Total + parsedExpr.Evaluate();
   }

   cout << "Sum(1, " << UpperBound << ", " << userExpression << ") = " << (long long)Total;
}
				
			
Sum(1, 1000000, x * 2 + 5) = 1000006000000
Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      Dim variableX = uc.DefineVariable("x")
      Dim userExpression = "x * 2 + 5"
      Dim Total = 0.0
      Dim UpperBound = 1000000 '// One million
      
      '// Parse the expression just once before the loop begins.
      Dim parsedExpr = uc.Parse(userExpression)
      
      Dim stopwatch = System.Diagnostics.Stopwatch.StartNew()
      For x  As Double = 1 To UpperBound
         variableX.Value(x)
         Total = Total + parsedExpr.Evaluate()
      Next
      stopwatch.Stop()
      '//Uncomment the following line to reveal the actual speed:
      '//Console.WriteLine($"Elapsed Milliseconds: {stopwatch.ElapsedMilliseconds} ms");
      
      Console.Write("Sum(1, ")
      Console.Write(UpperBound)
      Console.Write(", ")
      Console.Write(userExpression)
      Console.Write(") = ")
      Console.Write(Total)
   End Sub
End Module
				
			
Sum(1, 1000000, x * 2 + 5) = 1000006000000
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Illustrates the core relationship between the uCalc engine, an Item (variable), and a compiled Expression.

ID: 31

See: Evaluate, Introduction, Memory Management, Parse, Release, Release, The uCalc Object Model - A High-Level Overview, uCalc Fast Math Parser, Value(double) 
				
					using uCalcSoftware;

var uc = new uCalc();
var VariableX = uc.DefineVariable("x");
var Expression = "x^2 * 10"; // Replace this with your expression

Console.WriteLine("--- Efficient: Parse() once, then Evaluate() in a loop ---");
var ParsedExpr = uc.Parse(Expression);
for (double x = 1; x <= 10; x++) {
   VariableX.Value(x);
   Console.WriteLine(ParsedExpr.Evaluate());
}

ParsedExpr.Release();
VariableX.Release();
				
			
--- Efficient: Parse() once, then Evaluate() in a loop ---
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Explore 600+ other examples
				
					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   auto VariableX = uc.DefineVariable("x");
   auto Expression = "x^2 * 10"; // Replace this with your expression

   cout << "--- Efficient: Parse() once, then Evaluate() in a loop ---" << endl;
   auto ParsedExpr = uc.Parse(Expression);
   for (double x = 1; x <= 10; x++) {
      VariableX.Value(x);
      cout << ParsedExpr.Evaluate() << endl;
   }

   ParsedExpr.Release();
   VariableX.Release();
}
				
			
--- Efficient: Parse() once, then Evaluate() in a loop ---
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640
810
1000
Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      Dim VariableX = uc.DefineVariable("x")
      Dim Expression = "x^2 * 10" '// Replace this with your expression
      
      Console.WriteLine("--- Efficient: Parse() once, then Evaluate() in a loop ---")
      Dim ParsedExpr = uc.Parse(Expression)
      For x  As Double = 1 To 10
         VariableX.Value(x)
         Console.WriteLine(ParsedExpr.Evaluate())
      Next
      
      ParsedExpr.Release()
      VariableX.Release()
   End Sub
End Module
				
			
--- Efficient: Parse() once, then Evaluate() in a loop ---
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810
1000
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Evaluate() auto-conversion

ID: 96

See: Evaluate, EvaluateDbl 
				
					using uCalcSoftware;

var uc = new uCalc();
// The int return value type in MyExprB is converted to
// Double with .Evaluate(), but not with .EvaluateDbl()
var MyExprA = uc.Parse("3.2 + 5.2");
var MyExprB = uc.Parse("int(3.2 + 5.2)");

Console.WriteLine(MyExprA.Evaluate());
Console.WriteLine(MyExprA.EvaluateDbl() == 8.4);
Console.WriteLine(MyExprB.Evaluate());
Console.WriteLine(MyExprB.EvaluateDbl() == 8);
				
			
8.4
True
8
False
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

#define tf(IsTrue) ((IsTrue) ? "True" : "False")

int main() {
   uCalc uc;
   // The int return value type in MyExprB is converted to
   // Double with .Evaluate(), but not with .EvaluateDbl()
   auto MyExprA = uc.Parse("3.2 + 5.2");
   auto MyExprB = uc.Parse("int(3.2 + 5.2)");

   cout << MyExprA.Evaluate() << endl;
   cout << tf(MyExprA.EvaluateDbl() == 8.4) << endl;
   cout << MyExprB.Evaluate() << endl;
   cout << tf(MyExprB.EvaluateDbl() == 8) << endl;
}
				
			
8.4
True
8
False
Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      '// The int return value type in MyExprB is converted to
      '// Double with .Evaluate(), but not with .EvaluateDbl()
      Dim MyExprA = uc.Parse("3.2 + 5.2")
      Dim MyExprB = uc.Parse("int(3.2 + 5.2)")
      
      Console.WriteLine(MyExprA.Evaluate())
      Console.WriteLine(MyExprA.EvaluateDbl() = 8.4)
      Console.WriteLine(MyExprB.Evaluate())
      Console.WriteLine(MyExprB.EvaluateDbl() = 8)
   End Sub
End Module
				
			
8.4
True
8
False
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A minimal example demonstrating the basic 'Parse once, Evaluate many' pattern.

ID: 1192

See: Evaluate, Optimizing Performance in Loops 
				
					using uCalcSoftware;

var uc = new uCalc();
// 1. Parse the expression string once to create a reusable object.
//var expr = uc.Parse("5 * 10");
using (var expr = new uCalc.Expression("5 * 10")) {
   
   // 2. Evaluate the pre-parsed object as many times as needed.
   Console.WriteLine(expr.Evaluate());
   Console.WriteLine(expr.Evaluate());

} // The expression object is automatically released here.
				
			
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50
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   // 1. Parse the expression string once to create a reusable object.
   //var expr = uc.Parse("5 * 10");
   {
      uCalc::Expression expr("5 * 10");
      expr.Owned(); // Causes expr to be released when it goes out of scope

      // 2. Evaluate the pre-parsed object as many times as needed.
      cout << expr.Evaluate() << endl;
      cout << expr.Evaluate() << endl;

   } // The expression object is automatically released here.
}
				
			
50
50
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					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      '// 1. Parse the expression string once to create a reusable object.
      '//var expr = uc.Parse("5 * 10");
      Using expr As New uCalc.Expression("5 * 10")
         
         '// 2. Evaluate the pre-parsed object as many times as needed.
         Console.WriteLine(expr.Evaluate())
         Console.WriteLine(expr.Evaluate())
         
      End Using '// The expression object is automatically released here.
   End Sub
End Module
				
			
50
50
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Passing arg ByExpr (delayed lazy eval) and ByHandle

ID: 14

See: (Constructor), Arg, ArgExpr, ArgItem, DefineFunction, Evaluate, Introduction, Value(double) 
				
					using uCalcSoftware;

var uc = new uCalc();

static void MySum(uCalc.Callback cb) {
   var Total = 0.0;
   var Expr = cb.ArgExpr(1);
   var Start = cb.Arg(2);
   var Finish = cb.Arg(3);
   var Variable = cb.ArgItem(4);

   for (double x = Start; x <= Finish; x++) {
      Variable.Value(x);
      Total += Expr.Evaluate();
   }
   cb.Return(Total);
}

uc.DefineVariable("x");
uc.DefineFunction("Sum(ByExpr Expr, Start, Finish, ByHandle Var)", MySum);
Console.WriteLine(uc.Eval("Sum(x ^ 2, 1, 10, x)"));

				
			
385
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					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

void ucalc_call MySum(uCalcBase::Callback cb) {
   auto Total = 0.0;
   auto Expr = cb.ArgExpr(1);
   auto Start = cb.Arg(2);
   auto Finish = cb.Arg(3);
   auto Variable = cb.ArgItem(4);

   for (double x = Start; x <= Finish; x++) {
      Variable.Value(x);
      Total += Expr.Evaluate();
   }
   cb.Return(Total);
}
int main() {
   uCalc uc;
   uc.DefineVariable("x");
   uc.DefineFunction("Sum(ByExpr Expr, Start, Finish, ByHandle Var)", MySum);
   cout << uc.Eval("Sum(x ^ 2, 1, 10, x)") << endl;

}
				
			
385
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					Imports System
Imports uCalcSoftware
Public Module Program
   
   Public Sub MySum(ByVal cb As uCalc.Callback)
      Dim Total = 0.0
      Dim Expr = cb.ArgExpr(1)
      Dim Start = cb.Arg(2)
      Dim Finish = cb.Arg(3)
      Dim Variable = cb.ArgItem(4)
      
      For x  As Double = Start To Finish
         Variable.Value(x)
         Total += Expr.Evaluate()
      Next
      cb.Return(Total)
   End Sub
   Public Sub Main()
      Dim uc As New uCalc()
      uc.DefineVariable("x")
      uc.DefineFunction("Sum(ByExpr Expr, Start, Finish, ByHandle Var)", AddressOf MySum)
      Console.WriteLine(uc.Eval("Sum(x ^ 2, 1, 10, x)"))
      
   End Sub
End Module
				
			
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