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.

Project: Building a Basic Calculator UI

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A step-by-step tutorial on creating a functional calculator application, using uCalc's expression parser to handle the evaluation logic.

Remarks

💡 Project: Building a Basic Calculator UI

This project brings together the core concepts of the uCalc expression parser to build a familiar, practical application: a basic calculator. You'll see how to handle user input from a simple UI and let uCalc do all the heavy lifting of parsing and calculation with a single function call.

This tutorial is UI-framework-agnostic. Whether you're using WinForms, WPF, Qt, or a web framework, the core logic for interfacing with uCalc remains the same.

Prerequisites

  • Familiarity with the EvalStr method.
  • Basic knowledge of your chosen UI framework for creating buttons and a text display.

🖥️ Step 1: The User Interface

Every calculator needs a basic set of components:

  1. A Display: A read-only text box to show the current expression and the final result. Let's call it display_text.
  2. Number Buttons: Buttons for 0 through 9.
  3. Operator Buttons: Buttons for +, -, *, /.
  4. Action Buttons:
    • An Equals (=) button to trigger the calculation.
    • A Clear (C) button to reset the display.

The layout would look something like a standard pocket calculator.

🧠 Step 2: The Core Logic - Handling Button Clicks

The logic behind the UI is surprisingly simple. We'll manage a single string variable that represents the content of the calculator's display. The example below will simulate this process.

Number and Operator Buttons (0-9, +, -, *, /)

When a user clicks any of these buttons, the action is the same: append the button's character to the display_text string.

  • If the display shows "123", pressing + changes it to "123+".
  • If the display shows "123+", pressing 4 changes it to "123+4".

The Clear Button (C)

When the 'C' button is clicked, simply clear the display_text string to an empty string ("").

✨ Step 3: The Magic - The Equals Button (=)

This is where uCalc shines. When the user presses the = button, all you need to do is:

  1. Get the complete expression string from your display_text.
  2. Pass this string directly to the EvalStr method.
  3. Take the result from EvalStr and set it as the new content of display_text.

That's it! uCalc handles everything else:

  • It correctly parses the order of operations.
  • It performs the calculations.
  • If the user entered an invalid expression (like "5 * + 3"), EvalStr will return a descriptive error message (e.g., "Syntax error"), which you can display directly to the user.

💡 Why uCalc? (Comparative Analysis)

How would you do this without uCalc? You would need to build a complete parsing engine yourself. This typically involves complex algorithms like:

  • Shunting-yard algorithm: To convert the infix expression (5 + 2) into a postfix (Reverse Polish Notation) expression (5 2 +).
  • Postfix Evaluation: To evaluate the RPN expression using a stack.
  • State Management: To handle operator precedence, parentheses, and error states.

This can be hundreds of lines of complex, error-prone code. uCalc reduces this entire complex problem to a single line: result = uc.EvalStr(expression).

🚀 Step 4: Putting It All Together

The following example simulates the complete logic of the calculator's "brain". It shows how a string is built up from simulated button presses and then evaluated by uCalc.

Examples

Simulates the core logic of a calculator, showing how user input is built into an expression string and evaluated.

ID: 1365

See: Project: Building a Basic Calculator UI 
				
					using uCalcSoftware;

var uc = new uCalc();
string display_text = "";

// Simulate user pressing buttons: 1, 2, 3, +, 4, 5, 6
display_text = display_text + "123";
Console.WriteLine($"Display: {display_text}");

display_text = display_text + "+";
Console.WriteLine($"Display: {display_text}");

display_text = display_text + "456";
Console.WriteLine($"Display: {display_text}");

// Simulate pressing '='. This is where uCalc does the work.
var result = uc.EvalStr(display_text);
display_text = result;
Console.WriteLine($"Result: {display_text}");

Console.WriteLine("");

// Simulate a new calculation with an error
display_text = "5 * / 3";
Console.WriteLine($"Display: {display_text}");
result = uc.EvalStr(display_text);
display_text = result;
Console.WriteLine($"Result: {display_text}");

Console.WriteLine("");

// Simulate clearing the display
display_text = "C"; // Let's say 'C' is a special command
if (display_text == "C") {
   display_text = "";
}
Console.WriteLine($"Display after clear: '{display_text}'");
				
			
Display: 123
Display: 123+
Display: 123+456
Result: 579

Display: 5 * / 3
Result: Syntax error

Display after clear: ''
Explore 600+ other examples
				
					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   string display_text = "";

   // Simulate user pressing buttons: 1, 2, 3, +, 4, 5, 6
   display_text = display_text + "123";
   cout << "Display: " << display_text << endl;

   display_text = display_text + "+";
   cout << "Display: " << display_text << endl;

   display_text = display_text + "456";
   cout << "Display: " << display_text << endl;

   // Simulate pressing '='. This is where uCalc does the work.
   auto result = uc.EvalStr(display_text);
   display_text = result;
   cout << "Result: " << display_text << endl;

   cout << "" << endl;

   // Simulate a new calculation with an error
   display_text = "5 * / 3";
   cout << "Display: " << display_text << endl;
   result = uc.EvalStr(display_text);
   display_text = result;
   cout << "Result: " << display_text << endl;

   cout << "" << endl;

   // Simulate clearing the display
   display_text = "C"; // Let's say 'C' is a special command
   if (display_text == "C") {
      display_text = "";
   }
   cout << "Display after clear: '" << display_text << "'" << endl;
}
				
			
Display: 123
Display: 123+
Display: 123+456
Result: 579

Display: 5 * / 3
Result: Syntax error

Display after clear: ''
Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      Dim display_text As String = ""
      
      '// Simulate user pressing buttons: 1, 2, 3, +, 4, 5, 6
      display_text = display_text + "123"
      Console.WriteLine($"Display: {display_text}")
      
      display_text = display_text + "+"
      Console.WriteLine($"Display: {display_text}")
      
      display_text = display_text + "456"
      Console.WriteLine($"Display: {display_text}")
      
      '// Simulate pressing '='. This is where uCalc does the work.
      Dim result = uc.EvalStr(display_text)
      display_text = result
      Console.WriteLine($"Result: {display_text}")
      
      Console.WriteLine("")
      
      '// Simulate a new calculation with an error
      display_text = "5 * / 3"
      Console.WriteLine($"Display: {display_text}")
      result = uc.EvalStr(display_text)
      display_text = result
      Console.WriteLine($"Result: {display_text}")
      
      Console.WriteLine("")
      
      '// Simulate clearing the display
      display_text = "C" '// Let's say 'C' is a special command
      If display_text = "C" Then
         display_text = ""
      End If
      Console.WriteLine($"Display after clear: '{display_text}'")
   End Sub
End Module
				
			
Display: 123
Display: 123+
Display: 123+456
Result: 579

Display: 5 * / 3
Result: Syntax error

Display after clear: ''
Explore 600+ other examples