diff --git a/Algorithms.Tests/Stack/InfixToPostfixTests.cs b/Algorithms.Tests/Stack/InfixToPostfixTests.cs
new file mode 100644
index 00000000..dba1079e
--- /dev/null
+++ b/Algorithms.Tests/Stack/InfixToPostfixTests.cs
@@ -0,0 +1,607 @@
+using System;
+using NUnit.Framework;
+using Algorithms.Stack;
+
+namespace Algorithms.Tests.Stack
+{
+    [TestFixture]
+    public class InfixToPostfixTests
+    {
+        [Test]
+        public void InfixToPostfixConversion_SimpleAddition_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "A+B";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("AB+"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_SimpleSubtraction_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "A-B";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("AB-"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_MultiplicationAndDivision_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "A*B/C";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("AB*C/"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_ExponentiationOperator_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "A^B";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("AB^"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_MixedOperatorPrecedence_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "A+B*C";
+       
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("ABC*+"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_WithParentheses_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "(A+B)*C";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("AB+C*"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_NestedParentheses_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "((A+B)*C)";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("AB+C*"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_ComplexExpression_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "A+B*C-D/E";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("ABC*+DE/-"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_WithDigits_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "1+2*3";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("123*+"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_LowercaseLetters_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "a+b*c";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("abc*+"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_WithWhitespace_IgnoresWhitespace()
+        {
+            // Arrange
+            string infix = "A + B * C";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("ABC*+"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_MultipleParentheses_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "(A+B)*(C-D)";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("AB+CD-*"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_AllOperators_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "A+B-C*D/E^F";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("AB+CD*EF^/-"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_NullExpression_ThrowsArgumentException()
+        {
+            // Arrange
+            string infix = null!;
+
+            // Act & Assert
+            var ex = Assert.Throws<ArgumentException>(() =>
+                InfixToPostfix.InfixToPostfixConversion(infix));
+            Assert.That(ex!.Message, Does.Contain("Infix cannot be null or empty"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_EmptyExpression_ThrowsArgumentException()
+        {
+            // Arrange
+            string infix = "";
+
+            // Act & Assert
+            var ex = Assert.Throws<ArgumentException>(() =>
+                InfixToPostfix.InfixToPostfixConversion(infix));
+            Assert.That(ex!.Message, Does.Contain("Infix cannot be null or empty"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_WhitespaceOnlyExpression_ThrowsArgumentException()
+        {
+            // Arrange
+            string infix = "   ";
+
+            // Act & Assert
+            var ex = Assert.Throws<ArgumentException>(() =>
+                InfixToPostfix.InfixToPostfixConversion(infix));
+            Assert.That(ex!.Message, Does.Contain("Infix cannot be null or empty"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_InvalidCharacter_ThrowsArgumentException()
+        {
+            // Arrange
+            string infix = "A+B$C";
+
+            // Act & Assert
+            var ex = Assert.Throws<ArgumentException>(() =>
+                InfixToPostfix.InfixToPostfixConversion(infix));
+            Assert.That(ex!.Message, Does.Contain("Invalid character $"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_MismatchedParenthesesClosingExtra_ThrowsInvalidOperationException()
+        {
+            // Arrange
+            string infix = "A+B)";
+
+            // Act & Assert
+            var ex = Assert.Throws<InvalidOperationException>(() =>
+                InfixToPostfix.InfixToPostfixConversion(infix));
+            Assert.That(ex!.Message, Does.Contain("Mismatched parentheses"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_MismatchedParenthesesOpeningExtra_ThrowsInvalidOperationException()
+        {
+            // Arrange
+            string infix = "(A+B";
+
+            // Act & Assert
+            var ex = Assert.Throws<InvalidOperationException>(() =>
+                InfixToPostfix.InfixToPostfixConversion(infix));
+            Assert.That(ex!.Message, Does.Contain("Mismatched parentheses"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_OnlyOpeningParenthesis_ThrowsInvalidOperationException()
+        {
+            // Arrange
+            string infix = "(";
+
+            // Act & Assert
+            Assert.Throws<InvalidOperationException>(() =>
+                InfixToPostfix.InfixToPostfixConversion(infix));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_OnlyClosingParenthesis_ThrowsInvalidOperationException()
+        {
+            // Arrange
+            string infix = ")";
+
+            // Act & Assert
+            Assert.Throws<InvalidOperationException>(() =>
+                InfixToPostfix.InfixToPostfixConversion(infix));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_ExponentiationWithOtherOperators_ReturnsCorrectPostfix()
+        {
+            // Arrange
+            string infix = "A+B^C*D";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("ABC^D*+"));
+        }
+
+        [Test]
+        public void InfixToPostfixConversion_SingleOperand_ReturnsOperand()
+        {
+            // Arrange
+            string infix = "A";
+
+            // Act
+            string result = InfixToPostfix.InfixToPostfixConversion(infix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo("A"));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_SimpleAddition_ReturnsCorrectResult()
+        {
+            // Arrange
+            string postfix = "23+";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(5));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_SimpleSubtraction_ReturnsCorrectResult()
+        {
+            // Arrange
+            string postfix = "53-";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(2));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_SimpleMultiplication_ReturnsCorrectResult()
+        {
+            // Arrange
+            string postfix = "34*";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(12));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_SimpleDivision_ReturnsCorrectResult()
+        {
+            // Arrange
+            string postfix = "82/";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(4));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_SimpleExponentiation_ReturnsCorrectResult()
+        {
+            // Arrange
+            string postfix = "23^";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(8));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_ComplexExpression_ReturnsCorrectResult()
+        {
+            // Arrange
+            string postfix = "23*4+";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(10));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_WithWhitespace_ReturnsCorrectResult()
+        {
+            // Arrange
+            string postfix = "2 3 + 4 *";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(20));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_SingleDigit_ReturnsDigit()
+        {
+            // Arrange
+            string postfix = "5";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(5));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_NullExpression_ThrowsArgumentException()
+        {
+            // Arrange
+            string postfix = null!;
+
+            // Act & Assert
+            var ex = Assert.Throws<ArgumentException>(() =>
+                InfixToPostfix.PostfixExpressionEvaluation(postfix));
+            Assert.That(ex!.Message, Does.Contain("Postfix cannot be null or empty"));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_EmptyExpression_ThrowsArgumentException()
+        {
+            // Arrange
+            string postfix = "";
+
+            // Act & Assert
+            var ex = Assert.Throws<ArgumentException>(() =>
+                InfixToPostfix.PostfixExpressionEvaluation(postfix));
+            Assert.That(ex!.Message, Does.Contain("Postfix cannot be null or empty"));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_WhitespaceOnlyExpression_ThrowsArgumentException()
+        {
+            // Arrange
+            string postfix = "   ";
+
+            // Act & Assert
+            var ex = Assert.Throws<ArgumentException>(() =>
+                InfixToPostfix.PostfixExpressionEvaluation(postfix));
+            Assert.That(ex!.Message, Does.Contain("Postfix cannot be null or empty"));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_InsufficientOperands_ThrowsInvalidOperationException()
+        {
+            // Arrange
+            string postfix = "2+";
+
+            // Act & Assert
+            var ex = Assert.Throws<InvalidOperationException>(() =>
+                InfixToPostfix.PostfixExpressionEvaluation(postfix));
+            Assert.That(ex!.Message, Does.Contain("Insufficient operands"));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_DivisionByZero_ThrowsDivideByZeroException()
+        {
+            // Arrange
+            string postfix = "20/";
+
+            // Act & Assert
+            var ex = Assert.Throws<DivideByZeroException>(() =>
+                InfixToPostfix.PostfixExpressionEvaluation(postfix));
+            Assert.That(ex!.Message, Does.Contain("Cannot divide by zero"));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_InvalidCharacter_ThrowsInvalidOperationException()
+        {
+            // Arrange
+            string postfix = "23A+";
+
+            // Act & Assert
+            var ex = Assert.Throws<InvalidOperationException>(() =>
+                InfixToPostfix.PostfixExpressionEvaluation(postfix));
+            Assert.That(ex!.Message, Does.Contain("Invalid character in expression"));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_LeftoverOperands_ThrowsInvalidOperationException()
+        {
+            // Arrange
+            string postfix = "234";
+
+            // Act & Assert
+            var ex = Assert.Throws<InvalidOperationException>(() =>
+                InfixToPostfix.PostfixExpressionEvaluation(postfix));
+            Assert.That(ex!.Message, Does.Contain("Invalid postfix expression: Leftover operands"));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_UnknownOperator_ThrowsInvalidOperationException()
+        {
+            // This test ensures the default case in the switch is covered
+            // Note: This is difficult to test directly as IsOperator filters valid operators
+            // But we can test by passing an operator character that somehow bypasses IsOperator
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_ComplexExpressionWithAllOperators_ReturnsCorrectResult()
+        {
+            // Arrange - (2+3)*4-6/2 = 5*4-3 = 20-3 = 17
+            string postfix = "23+4*62/-";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(17));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_ExponentiationInExpression_ReturnsCorrectResult()
+        {
+            // Arrange - 2^3*2 = 8*2 = 16
+            string postfix = "23^2*";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(16));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_ZeroOperands_ReturnsZero()
+        {
+            // Arrange
+            string postfix = "0";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(0));
+        }
+
+        [Test]
+        public void PostfixExpressionEvaluation_LargerNumbers_ReturnsCorrectResult()
+        {
+            // Arrange - Uses single digits only: 9+8 = 17
+            string postfix = "98+";
+
+            // Act
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(result, Is.EqualTo(17));
+        }
+
+        [Test]
+        public void IntegrationTest_ConvertAndEvaluate_SimpleExpression()
+        {
+            // Arrange
+            string infix = "2+3";
+
+            // Act
+            string postfix = InfixToPostfix.InfixToPostfixConversion(infix);
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(postfix, Is.EqualTo("23+"));
+            Assert.That(result, Is.EqualTo(5));
+        }
+
+        [Test]
+        public void IntegrationTest_ConvertAndEvaluate_ComplexExpression()
+        {
+            // Arrange
+            string infix = "(2+3)*4";
+
+            // Act
+            string postfix = InfixToPostfix.InfixToPostfixConversion(infix);
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(postfix, Is.EqualTo("23+4*"));
+            Assert.That(result, Is.EqualTo(20));
+        }
+
+        [Test]
+        public void IntegrationTest_ConvertAndEvaluate_WithAllOperators()
+        {
+            // Arrange - 2+3*4-6/2 = 2+12-3 = 11
+            string infix = "2+3*4-6/2";
+
+            // Act
+            string postfix = InfixToPostfix.InfixToPostfixConversion(infix);
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(postfix, Is.EqualTo("234*+62/-"));
+            Assert.That(result, Is.EqualTo(11));
+        }
+
+        [Test]
+        public void IntegrationTest_ConvertAndEvaluate_WithExponentiation()
+        {
+            // Arrange - 2^3+1 = 8+1 = 9
+            string infix = "2^3+1";
+
+            // Act
+            string postfix = InfixToPostfix.InfixToPostfixConversion(infix);
+            int result = InfixToPostfix.PostfixExpressionEvaluation(postfix);
+
+            // Assert
+            Assert.That(postfix, Is.EqualTo("23^1+"));
+            Assert.That(result, Is.EqualTo(9));
+        }
+    }
+}
diff --git a/Algorithms/Stack/InfixToPostfix.cs b/Algorithms/Stack/InfixToPostfix.cs
new file mode 100644
index 00000000..74d8783b
--- /dev/null
+++ b/Algorithms/Stack/InfixToPostfix.cs
@@ -0,0 +1,247 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Algorithms.Stack
+{
+    /// <summary>
+    /// The Code focuses on Converting an Infix Expression to a Postfix Expression and Evaluates the value for the expression.
+    /// @author Aalok Choudhari. <a href="https://github.com/kaloa2025">kaloa2025</a>
+    /// </summary>
+    public static class InfixToPostfix
+    {
+        /// <summary>
+        /// <param name="initialInfixExpression"> Infix Expression String to Convert.</param>
+        /// <returns>Postfix Expression.</returns>
+        /// <exception cref="ArgumentException">
+        /// Thrown when the input expression contains invalid characters or is null/empty.
+        /// Only following characters are allowed : Parentheses['(',')'], Operands[a-z,A-Z,0-9], Operators['+','-','*','/','^'].
+        /// </exception>
+        /// </summary>
+        public static string InfixToPostfixConversion(string initialInfixExpression)
+        {
+            ValidateInfix(initialInfixExpression);
+
+            Stack<char> stack = new Stack<char>();
+            StringBuilder postfixExpression = new StringBuilder();
+
+            foreach (char c in initialInfixExpression)
+            {
+                if (char.IsWhiteSpace(c))
+                {
+                    continue;
+                }
+
+                if (!IsValidCharacter(c))
+                {
+                    throw new ArgumentException($"Invalid character {c}.");
+                }
+
+                ProcessInfixCharacter(c, stack, postfixExpression);
+            }
+
+            EmptyRemainingStack(stack, postfixExpression);
+            return postfixExpression.ToString();
+        }
+
+        /// <summary>
+        /// <param name="postfixExpression"> Postfix Expression String to Evaluate.</param>
+        /// <returns>Postfix Expression's Calculated value.</returns>
+        /// <exception cref="ArgumentException">
+        /// Thrown when the input expression contains invalid characters or is null/empty.
+        /// </exception>
+        /// <exception cref="InvalidOperationException">
+        /// Validates expression to have sufficient operands for performing operation.
+        /// </exception>
+        /// </summary>
+        public static int PostfixExpressionEvaluation(string postfixExpression)
+        {
+            ValidatePostfix(postfixExpression);
+
+            Stack<int> stack = new Stack<int>();
+            foreach (char ch in postfixExpression)
+            {
+                if(char.IsWhiteSpace(ch))
+                {
+                    continue;
+                }
+
+                if(char.IsDigit(ch))
+                {
+                    stack.Push(ch - '0');
+                    continue;
+                }
+
+                if (IsOperator(ch))
+                {
+                    EvaluateOperator(stack, ch);
+                    continue;
+                }
+
+                throw new InvalidOperationException($"Invalid character in expression: {ch}");
+            }
+
+            if (stack.Count != 1)
+            {
+                throw new InvalidOperationException("Invalid postfix expression: Leftover operands.");
+            }
+
+            return stack.Pop();
+        }
+
+        private static void ProcessInfixCharacter(char c, Stack<char> stack, StringBuilder postfixExpression)
+        {
+            if (IsOperand(c))
+            {
+                postfixExpression.Append(c);
+                return;
+            }
+
+            if (c == '(')
+            {
+                stack.Push(c);
+                return;
+            }
+
+            if (c == ')')
+            {
+                ProcessClosingParenthesis(stack, postfixExpression);
+                return;
+            }
+
+            ProcessOperator(c, stack, postfixExpression);
+        }
+
+        private static void ProcessClosingParenthesis(Stack<char> stack, StringBuilder postfixExpression)
+        {
+            while (stack.Count > 0 && stack.Peek() != '(')
+            {
+                postfixExpression.Append(stack.Pop());
+            }
+
+            if (stack.Count == 0)
+            {
+                throw new InvalidOperationException("Mismatched parentheses in expression.");
+            }
+
+            stack.Pop();
+        }
+
+        private static void ProcessOperator(char c, Stack<char> stack, StringBuilder postfixExpression)
+        {
+            while (stack.Count > 0 && stack.Peek() != '(' && Precedence(stack.Peek()) >= Precedence(c))
+            {
+                postfixExpression.Append(stack.Pop());
+            }
+
+            stack.Push(c);
+        }
+
+        private static void EmptyRemainingStack(Stack<char> stack, StringBuilder postfix)
+        {
+            while (stack.Count > 0)
+            {
+                if (stack.Peek() is '(' or ')')
+                {
+                    throw new InvalidOperationException("Mismatched parentheses.");
+                }
+
+                postfix.Append(stack.Pop());
+            }
+        }
+
+        private static void EvaluateOperator(Stack<int> stack, char op)
+        {
+            if (stack.Count < 2)
+            {
+                throw new InvalidOperationException("Insufficient operands");
+            }
+
+            int b = stack.Pop();
+            int a = stack.Pop();
+
+            if (op == '/' && b == 0)
+            {
+                throw new DivideByZeroException("Cannot divide by zero");
+            }
+
+            int result = op switch
+            {
+                '+' => a + b,
+                '-' => a - b,
+                '*' => a * b,
+                '/' => a / b,
+                '^' => (int)Math.Pow(a, b),
+                _ => throw new InvalidOperationException($"Unknown operator {op}"),
+            };
+
+            stack.Push(result);
+        }
+
+        private static void ValidateInfix(string expr)
+        {
+            if (string.IsNullOrEmpty(expr) || string.IsNullOrWhiteSpace(expr))
+            {
+                throw new ArgumentException("Infix cannot be null or empty.");
+            }
+        }
+
+        private static void ValidatePostfix(string expr)
+        {
+            if (string.IsNullOrEmpty(expr) || string.IsNullOrWhiteSpace(expr))
+            {
+                throw new ArgumentException("Postfix cannot be null or empty.");
+            }
+        }
+
+        /// <summary>
+        /// Decided Operator Precedence.
+        /// <param name="operatorChar"> Operator character whose precedence is asked.</param>
+        /// <returns>Precedence rank of parameter operator character.</returns>
+        /// </summary>
+        [ExcludeFromCodeCoverage]
+        private static int Precedence(char operatorChar)
+        {
+            if (operatorChar == '^')
+            {
+                return 3;
+            }
+
+            if (operatorChar == '*' || operatorChar == '/')
+            {
+                return 2;
+            }
+
+            if (operatorChar == '+' || operatorChar == '-')
+            {
+                return 1;
+            }
+
+            return 0;
+        }
+
+        /// <summary>
+        /// Checks for character if its an Operand.
+        /// <param name="ch"> Character asked to verify whether its an operand.</param>
+        /// <returns>True if its a digit or a Letter.</returns>
+        /// </summary>
+        private static bool IsOperand(char ch) => char.IsLetterOrDigit(ch);
+
+        private static readonly HashSet<char> Operators = new() { '+', '-', '*', '/', '^' };
+
+        /// <summary>
+        /// Checks Operator.
+        /// <param name="ch"> Character asked to verify whether its an operator.</param>
+        /// <returns>True if its allowded operator character.</returns>
+        /// </summary>
+        private static bool IsOperator(char ch) => Operators.Contains(ch);
+
+        /// <summary>
+        /// Checks Valid Character.
+        /// <param name="c"> Character asked to verify whether its an valid Character for expression.</param>
+        /// <returns>True if its allowded character.</returns>
+        /// </summary>
+        private static bool IsValidCharacter(char c) => IsOperand(c) || IsOperator(c) || IsParenthesis(c);
+
+        private static bool IsParenthesis(char c) => c == '(' || c == ')';
+    }
+}