Task: Penney's game
C: #include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define SEQLEN 3

int getseq(char *s)
{
    int r = 0;
    int i = 1 << (SEQLEN - 1);

    while (*s && i) {
        switch (*s++) {
            case 'H':
            case 'h':
                r |= i;
                break;
            case 'T':
            case 't':
                
                break;
            default:
                return -1;
        }
        i >>= 1;
    }

    return r;
}

void printseq(int seq)
{
    int i;
    for (i = SEQLEN - 1; i >= 0; --i)
        printf("%c", seq & (1 << i) ? 'h' : 't');
}

int getuser(void)
{
    int user;
    char s[SEQLEN + 1];

    printf("Enter your sequence of %d (h/t): ", SEQLEN);
    while (1) {
        
        if (scanf("%3s", s) != 1) exit(1);
        if ((user = getseq(s)) != -1) return user;
        printf("Please enter only h/t characters: ");
    }
}

int getai(int user)
{
    int ai;

    printf("Computers sequence of %d is: ", SEQLEN);
    
    if (user == -1)
        ai = rand() & (1 << SEQLEN) - 1;
    else
        ai = (user >> 1) | ((~user << 1) & (1 << SEQLEN - 1));

    printseq(ai);
    printf("\n");
    return ai;
}

int rungame(int user, int ai)
{
    
    int last3 = rand() & (1 << SEQLEN) - 1;

    printf("Tossed sequence: ");
    printseq(last3);
    while (1) {
        if (user == last3) {
            printf("\nUser wins!\n");
            return 1;
        }

        if (ai == last3) {
            printf("\nAi wins!\n");
            return 0;
        }

        last3 = ((last3 << 1) & (1 << SEQLEN) - 2) | (rand() & 1);
        printf("%c", last3 & 1 ? 'h' : 't');
    }
}

int main(void)
{
    srand(time(NULL));
    int playerwins = 0;
    int totalgames = 0;

    
    while (1) {
        int user = -1;
        int ai   = -1;

        printf("\n");
        if (rand() & 1) {
            ai   = getai(user);
            user = getuser();
        }
        else {
            user = getuser();
            ai   = getai(user);
        }
        
        playerwins += rungame(user, ai);
        totalgames++;

        printf("You have won %d out of %d games\n", playerwins, totalgames);
        printf("=================================\n");
    }

    return 0;
}

C#: using static System.Console;
using static System.Threading.Thread;
using System;

public static class PenneysGame
{
    const int pause = 500;
    const int N = 3;
    static Random rng = new Random();

    static int Toss() => rng.Next(2);

    static string AsString(this int sequence) {
        string s = "";
        for (int b = 0b100; b > 0; b >>= 1) {
            s += (sequence & b) > 0 ? 'T' : 'H';
        }
        return s;
    }

    static int UserInput() {
        while (true) {
            switch (ReadKey().Key) {
                case ConsoleKey.Escape: return -1;
                case ConsoleKey.H: return 0;
                case ConsoleKey.T: return 1;
            }
            Console.Write('\b');
        }
    }

    public static void Main2() {
        int yourScore = 0, myScore = 0;
        while (true) {
            WriteLine($"Your score: {yourScore}, My score: {myScore}");
            WriteLine("Determining who goes first...");
            Sleep(pause);
            bool youStart = Toss() == 1;
            WriteLine(youStart ? "You go first." : "I go first.");
            int yourSequence = 0, mySequence = 0;
            if (youStart) {
                WriteLine("Choose your sequence of (H)eads and (T)ails (or press Esc to exit)");
                int userChoice;
                for (int i = 0; i < N; i++) {
                    if ((userChoice = UserInput()) < 0) return;
                    yourSequence = (yourSequence << 1) + userChoice;
                }
                mySequence = ((~yourSequence << 1) & 0b100) | (yourSequence >> 1);
            } else {
                for (int i = 0; i < N; i++) {
                    mySequence = (mySequence << 1) + Toss();
                }

                WriteLine("I chose " + mySequence.AsString());
                do {
                    WriteLine("Choose your sequence of (H)eads and (T)ails (or press Esc to exit)");
                    int choice;
                    yourSequence = 0;
                    for (int i = 0; i < N; i++) {
                        if ((choice = UserInput()) < 0) return;
                        yourSequence = (yourSequence << 1) + choice;
                    }
                    if (yourSequence == mySequence) {
                        WriteLine();
                        WriteLine("You cannot choose the same sequence.");
                    }
                } while (yourSequence == mySequence);
            }

            WriteLine();
            WriteLine($"Your sequence: {yourSequence.AsString()}, My sequence: {mySequence.AsString()}");
            WriteLine("Tossing...");
            int sequence = 0;
            for (int i = 0; i < N; i++) {
                Sleep(pause);
                int toss = Toss();
                sequence = (sequence << 1) + toss;
                Write(toss > 0 ? 'T' : 'H');
            }
            while (true) {
                if (sequence == yourSequence) {
                    WriteLine();
                    WriteLine("You win!");
                    yourScore++;
                    break;
                } else if (sequence == mySequence) {
                    WriteLine();
                    WriteLine("I win!");
                    myScore++;
                    break;
                }
                Sleep(pause);
                int toss = Toss();
                sequence = ((sequence << 1) + toss) & 0b111;
                Write(toss > 0 ? 'T' : 'H');
            }
            WriteLine("Press a key.");
            ReadKey();
            Clear();
        }
    }

}