CENG 342 - HW1: Rock-Paper-Scissors Game with MPI

Student: Suleyman Fatih Sert - 22050111031
Course: CENG 342 - Parallel Programming
Date: March 2026

Project Description

This project implements a Rock-Paper-Scissors game using MPI (Message Passing Interface) with 2 processes. The program supports two different communication modes to demonstrate distributed memory parallel programming concepts.

Game Rules

• Rock beats Scissors
• Scissors beats Paper
• Paper beats Rock
• If both processes choose the same move, the result is a draw and the round is replayed
• The game continues until one process reaches 5 points

Communication Modes

Mode 0 - Point-to-Point (P2P)

Uses MPI_Send and MPI_Recv for direct communication between processes:

• Process 1 sends its move to Process 0 using MPI_Send (tag 20)
• Process 0 (referee) receives the move with MPI_Recv, determines the winner, updates the score, and prints the results
• Process 0 sends the game status (continue/stop) back to Process 1 using MPI_Send (tag 30)

Mode 1 - Collective Communication

Uses MPI_Gather and MPI_Bcast for group communication:

• MPI_Gather collects both processes' moves at Process 0
• Process 0 evaluates the round and updates the score
• MPI_Bcast broadcasts the game status (continue/stop) to all processes

Program Structure

Function	Description
move_name()	Converts move integer (0,1,2) to string (ROCK, PAPER, SCISSORS)
find_winner()	Determines the winner of a round (0=draw, 1=P0 wins, 2=P1 wins)
play_p2p()	Runs the game using point-to-point communication
play_collective()	Runs the game using collective communication
main()	Initializes MPI, handles mode selection, and starts the game

Process Roles

• Process 0 (Referee): Receives moves, determines winners, tracks score, prints all output
• Process 1 (Player): Generates random moves and sends them to Process 0

Random Number Generation

Each process uses a different seed for random number generation:

srand(time(NULL) + rank * 100);

This ensures that both processes generate independent random moves in each run.

Files

File	Description
game.c	Main source code
Makefile	Build configuration
report.pdf	Project report with screenshots
hw1_p2p.png	Screenshot of P2P mode run
hw1_collective.png	Screenshot of Collective mode run
hw1_general.png	Screenshot of general run

Build & Run

make
mpirun -n 2 ./game

Example Output

The game starts
Select mode: 0 (P2P) or 1 (Collective)
0
Mode: 0
Turn 1, Process-0: ROCK, Process-1: PAPER
Process-1 wins, Score: 0 - 1
Turn 2, Process-0: SCISSORS, Process-1: SCISSORS
Draw! Replaying...
Turn 3, Process-0: PAPER, Process-1: ROCK
Process-0 wins, Score: 1 - 1
...
Process-1 has won the game with score: 5 - 3 in 9 turns.
The game ends

Screenshots

P2P Mode

Collective Mode

General Run