Task: Truth table
C#: using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class TruthTable
{
    enum TokenType { Unknown, WhiteSpace, Constant, Operand, Operator, LeftParenthesis, RightParenthesis }

    readonly char trueConstant, falseConstant;
    readonly IDictionary<char, Operator> operators = new Dictionary<char, Operator>();

    public TruthTable(char falseConstant, char trueConstant)
    {
        this.trueConstant = trueConstant;
        this.falseConstant = falseConstant;
        Operators = new OperatorCollection(operators);
    }

    public OperatorCollection Operators { get; }

    public void PrintTruthTable(string expression, bool isPostfix = false)
    {
        try {
            foreach (string line in GetTruthTable(expression, isPostfix)) {
                Console.WriteLine(line);
            }
        } catch (ArgumentException ex) {
            Console.WriteLine(expression + "   " + ex.Message);
        }
    }

    public IEnumerable<string> GetTruthTable(string expression, bool isPostfix = false)
    {
        if (string.IsNullOrWhiteSpace(expression)) throw new ArgumentException("Invalid expression.");
        
        
        var parameters = expression
            .Where(c => TypeOf(c) == TokenType.Operand)
            .Distinct()
            .Reverse()
            .Select((c, i) => (symbol: c, index: i))
            .ToDictionary(p => p.symbol, p => p.index);

        int count = parameters.Count;
        if (count > 32) throw new ArgumentException("Cannot have more than 32 parameters.");
        string header = count == 0 ? expression : string.Join(" ",
            parameters.OrderByDescending(p => p.Value).Select(p => p.Key)) + " " + expression;

        if (!isPostfix) expression = ConvertToPostfix(expression);

        var values = default(BitSet);
        var stack = new Stack<char>(expression.Length);
        for (int loop = 1 << count; loop > 0; loop--) {
            foreach (char token in expression) stack.Push(token);
            bool result = Evaluate(stack, values, parameters);
            if (header != null) {
                if (stack.Count > 0) throw new ArgumentException("Invalid expression.");
                yield return header;
                header = null;
            }
            string line = (count == 0 ? "" : " ") + (result ? trueConstant : falseConstant);
            line = string.Join(" ", Enumerable.Range(0, count)
                .Select(i => values[count - i - 1] ? trueConstant : falseConstant)) + line;
            yield return line;
            values++;
        }
    }

    public string ConvertToPostfix(string infix)
    {
        var stack = new Stack<char>();
        var postfix = new StringBuilder();
        foreach (char c in infix) {
            switch (TypeOf(c)) {
            case TokenType.WhiteSpace:
                continue;
            case TokenType.Constant:
            case TokenType.Operand:
                postfix.Append(c);
                break;
            case TokenType.Operator:
                int precedence = Precedence(c);
                while (stack.Count > 0 && Precedence(stack.Peek()) > precedence) {
                    postfix.Append(stack.Pop());
                }
                stack.Push(c);
                break;
            case TokenType.LeftParenthesis:
                stack.Push(c);
                break;
            case TokenType.RightParenthesis:
                char top = default(char);
                while (stack.Count > 0) {
                    top = stack.Pop();
                    if (top == '(') break;
                    else postfix.Append(top);
                }
                if (top != '(') throw new ArgumentException("No matching left parenthesis.");
                break;
            default:
                throw new ArgumentException("Invalid character: " + c);
            }
        }
        while (stack.Count > 0) {
            char top = stack.Pop();
            if (top == '(') throw new ArgumentException("No matching right parenthesis.");
            postfix.Append(top);
        }
        return postfix.ToString();
    }

    private bool Evaluate(Stack<char> expression, BitSet values, IDictionary<char, int> parameters)
    {
        if (expression.Count == 0) throw new ArgumentException("Invalid expression.");
        char c = expression.Pop();
        TokenType type = TypeOf(c);
        while (type == TokenType.WhiteSpace) type = TypeOf(c = expression.Pop());
        switch (type) {
        case TokenType.Constant:
            return c == trueConstant;
        case TokenType.Operand:
            return values[parameters[c]];
        case TokenType.Operator:
            bool right = Evaluate(expression, values, parameters);
            Operator op = operators[c];
            if (op.Arity == 1) return op.Function(right, right);
            bool left = Evaluate(expression, values, parameters);
            return op.Function(left, right);
        default:
            throw new ArgumentException("Invalid character: " + c);
        }
    }

    private TokenType TypeOf(char c)
    {
        if (char.IsWhiteSpace(c)) return TokenType.WhiteSpace;
        if (c == '(') return TokenType.LeftParenthesis;
        if (c == ')') return TokenType.RightParenthesis;
        if (c == trueConstant || c == falseConstant) return TokenType.Constant;
        if (operators.ContainsKey(c)) return TokenType.Operator;
        if (char.IsLetter(c)) return TokenType.Operand;
        return TokenType.Unknown;
    }

    private int Precedence(char op) => operators.TryGetValue(op, out var o) ? o.Precedence : int.MinValue;
}

struct Operator
{
    public Operator(char symbol, int precedence, Func<bool, bool> function) : this(symbol, precedence, 1, (l, r) => function(r)) { }

    public Operator(char symbol, int precedence, Func<bool, bool, bool> function) : this(symbol, precedence, 2, function) { }

    private Operator(char symbol, int precedence, int arity, Func<bool, bool, bool> function) : this()
    {
        Symbol = symbol;
        Precedence = precedence;
        Arity = arity;
        Function = function;
    }

    public char Symbol { get; }
    public int Precedence { get; }
    public int Arity { get; }
    public Func<bool, bool, bool> Function { get; }
}

public class OperatorCollection : IEnumerable
{
    readonly IDictionary<char, Operator> operators;

    internal OperatorCollection(IDictionary<char, Operator> operators) {
        this.operators = operators;
    }

    public void Add(char symbol, int precedence, Func<bool, bool> function)
        => operators[symbol] = new Operator(symbol, precedence, function);
    public void Add(char symbol, int precedence, Func<bool, bool, bool> function)
        => operators[symbol] = new Operator(symbol, precedence, function);

    public void Remove(char symbol) => operators.Remove(symbol);

    IEnumerator IEnumerable.GetEnumerator() => operators.Values.GetEnumerator();
}

struct BitSet
{
    private int bits;

    private BitSet(int bits) { this.bits = bits; }

    public static BitSet operator ++(BitSet bitSet) => new BitSet(bitSet.bits + 1);

    public bool this[int index] => (bits & (1 << index)) != 0;
}

class Program
{
    public static void Main() {
        TruthTable tt = new TruthTable('F', 'T') {
            Operators = {
                { '!', 6, r => !r },
                { '&', 5, (l, r) => l && r },
                { '^', 4, (l, r) => l ^ r },
                { '|', 3, (l, r) => l || r }
            }
        };
        
        var rng = new Random();
        tt.Operators.Add('?', 6, r => rng.NextDouble() < 0.5);
        string[] expressions = {
            "!!!T",
            "?T",
            "F & x | T",
            "F & (x | T",
            "F & x | T)",
            "a ! (a & a)",
            "a | (a * a)",
            "a ^ T & (b & !c)",
        };
        foreach (string expression in expressions) {
            tt.PrintTruthTable(expression);
            Console.WriteLine();
        }

        
        tt = new TruthTable('0', '1') {
            Operators = {
                { '-', 6, r => !r },
                { '^', 5, (l, r) => l && r },
                { 'v', 3, (l, r) => l || r },
                { '>', 2, (l, r) => !l || r },
                { '=', 1, (l, r) => l == r },
            }
        };
        expressions = new[] {
            "-X v 0 = X ^ 1",
            "(H > M) ^ (S > H) > (S > M)"
        };
        foreach (string expression in expressions) {
            tt.PrintTruthTable(expression);
            Console.WriteLine();
        }
    }
}

C++: #include <iostream>
#include <stack>
#include <string>
#include <sstream>
#include <vector>

struct var {
    char name;
    bool value;
};
std::vector<var> vars;

template<typename T>
T pop(std::stack<T> &s) {
    auto v = s.top();
    s.pop();
    return v;
}

bool is_operator(char c) {
    return c == '&' || c == '|' || c == '!' || c == '^';
}

bool eval_expr(const std::string &expr) {
    std::stack<bool> sob;
    for (auto e : expr) {
        if (e == 'T') {
            sob.push(true);
        } else if (e == 'F') {
            sob.push(false);
        } else {
           auto it = std::find_if(vars.cbegin(), vars.cend(), [e](const var &v) { return v.name == e; });
           if (it != vars.cend()) {
               sob.push(it->value);
           } else {
               int before = sob.size();
               switch (e) {
               case '&':
                   sob.push(pop(sob) & pop(sob));
                   break;
               case '|':
                   sob.push(pop(sob) | pop(sob));
                   break;
               case '!':
                   sob.push(!pop(sob));
                   break;
               case '^':
                   sob.push(pop(sob) ^ pop(sob));
                   break;
               default:
                   throw std::exception("Non-conformant character in expression.");
               }
           }
        }
    }
    if (sob.size() != 1) {
        throw std::exception("Stack should contain exactly one element.");
    }
    return sob.top();
}

void set_vars(int pos, const std::string &expr) {
    if (pos > vars.size()) {
        throw std::exception("Argument to set_vars can't be greater than the number of variables.");
    }
    if (pos == vars.size()) {
        for (auto &v : vars) {
            std::cout << (v.value ? "T  " : "F  ");
        }
        std::cout << (eval_expr(expr) ? 'T' : 'F') << '\n'; 
    } else {
        vars[pos].value = false;
        set_vars(pos + 1, expr);
        vars[pos].value = true;
        set_vars(pos + 1, expr);
    }
}


std::string process_expr(const std::string &src) {
    std::stringstream expr;

    for (auto c : src) {
        if (!isspace(c)) {
            expr << (char)toupper(c);
        }
    }

    return expr.str();
}

int main() {
    std::cout << "Accepts single-character variables (except for 'T' and 'F',\n";
    std::cout << "which specify explicit true or false values), postfix, with\n";
    std::cout << "&|!^ for and, or, not, xor, respectively; optionally\n";
    std::cout << "seperated by whitespace. Just enter nothing to quit.\n";

    while (true) {
        std::cout << "\nBoolean expression: ";

        std::string input;
        std::getline(std::cin, input);

        auto expr = process_expr(input);
        if (expr.length() == 0) {
            break;
        }

        vars.clear();
        for (auto e : expr) {
            if (!is_operator(e) && e != 'T' && e != 'F') {
                vars.push_back({ e, false });
            }
        }
        std::cout << '\n';
        if (vars.size() == 0) {
            std::cout << "No variables were entered.\n";
        } else {
            for (auto &v : vars) {
                std::cout << v.name << "  ";
            }
            std::cout << expr << '\n';

            auto h = vars.size() * 3 + expr.length();
            for (size_t i = 0; i < h; i++) {
                std::cout << '=';
            }
            std::cout << '\n';

            set_vars(0, expr);
        }
    }

    return 0;
}