elo.cpp

// CPP program for Elo Rating
#include <iostream>
#include <math.h>
using namespace std;
static float Ra = 2500, Rb = 2200;

// Function to calculate the Probability
float Probability(int rating1, int rating2)
{
    return 1.0 * 1.0 / (1 + 1.0 * pow(10, 1.0 * (rating1 - rating2) / 400));
}

// Function to calculate Elo rating
// K is a constant.
// d determines whether Player A wins or Player B.
void EloRating(float Ra, float Rb, int K, bool d)
{

    // To calculate the Winning
    // Probability of Player B
    float Pb = Probability(Ra, Rb);

    // To calculate the Winning
    // Probability of Player A
    float Pa = Probability(Rb, Ra);

    // Case -1 When Player A wins
    // Updating the Elo Ratings
    if (d == 1)
    {
        Ra = Ra + K * (1 - Pa);
        Rb = Rb + K * (0 - Pb);
    }

    // Case -2 When Player B wins
    // Updating the Elo Ratings
    else
    {
        Ra = Ra + K * (0 - Pa);
        Rb = Rb + K * (1 - Pb);
    }

    cout << "Updated Ratings:-\n";
    cout << "Ra = " << Ra << " Rb = " << Rb;
}

int main()
{
    // Ra and Rb are current ELO ratings

    int K = 30;
    bool d = 1;
    EloRating(Ra, Rb, K, d);

    return 0;
}