Monty Hall problem with gnuplot

Makefile

P=monty
OBJECTS=
CFLAGS = -g -Iinclude -Wall `pkg-config --cflags libsodium`
LDLIBS= `pkg-config --libs libsodium`
CC=cc

$(P): $(OBJECTS)

clean:
	-rm $(OBJECTS) $(P)

monty.c

#include <stdio.h>
#include <sodium.h>
#include <unistd.h>

int main(int argc, char **argv)
{
    if (sodium_init() < 0)
    {
        printf("Cannot initialize sodium");
        return 1;
    }
    int opt, doors = 3, attempts = 10;
    while((opt = getopt(argc, argv, "d:a:")) != -1)
    {
        switch(opt)
        {
            case 'd': doors = atoi(optarg); break;
            case 'a': attempts = atoi(optarg); break;
        }
    }
    printf("USAGE :\n\t%s -d [int doors > 3] "
           "-a [int attempts > 1] | gnuplot --persist\n", argv[0]);
    if (doors < 3 || attempts < 1) return 1;
    int first_choice_wins = 0, second_choice_wins = 0;
    FILE *fcw = fopen("fcw.csv", "w+"), *scw = fopen("scw.csv", "w+");
    for (int i = 0; i < attempts; i++)
    {
        int car = randombytes_uniform(doors);
        int player_first_choice = randombytes_uniform(doors);
        if (player_first_choice == car)
            first_choice_wins++;
        second_choice_wins++;
        fprintf(fcw, "%d, %d\n", i + 1, first_choice_wins);
        fprintf(scw, "%d, %d\n", i + 1, second_choice_wins);
    }
    fclose(fcw);
    fclose(scw);
    printf("set colorsequence classic\n");
    printf("set title 'Monty Hall paradox with %d doors and %d attempts'\n",
           doors, attempts);
    puts("set xlabel 'attempts'\nset ylabel 'total wins count'");
    printf("set xrange[0:%d]\n", attempts + 1);
    printf("set yrange[0:%d]\n", attempts + 1);
    puts("plot 'fcw.csv' with lines lw 5 lc rgb 'blue', "
         "'scw.csv' with lines lw 5 lc rgb 'red'\n");
    return 0;
}