C Mathematic Game

/**
 * a game where you need to claculate right the mathemathical equations that appears
 * the game counts points
 * +1 point for right answer -2 points for wrong answer
 * the game ends when the player arrives to 15 points
 * */

#define _XOPEN_SOURCE 500

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <string.h>

// function prototype
void clear (void);
void showscore (int);
char opera (int, int, int, int*);
int clean_stdin (void);


int main(void)
{
    // clear the screen
    clear();

    // variables used in program
    // var1 and var2 = math problam varibales
    // input = user input
    // seed = math opartion generator
    // hardness = game dificulty chooser
    // result = right answer
    // score = user score counter
    // wac, rac = "wrong answer counter", "right answer counter"
    int var1, var2, input, seed, hardness, result = 0, score = 0, wac = 0, rac = 0;

    // op = "opartion" - char holder for printing: '-' || '+' || 'X'
    // check = checking character in loops to make sure correct input is inserted
    char op = '\0', check;

    // game difficulty chooser - 3 options
    // 1 = var1 && var2 <=10 | 2 = var1 && var2 <= 15 | 3 = var1 && var2 <= 20
    do
    {
        clear();
        printf("Get 15 Points to Win!\nChoose Difficulty:\nEASY: 1     MEDIUM: 2       HARD: 3\n");
    }
    // makes sure input is a positive number between 1 and 3, if not, cleans stdin
    while(((scanf("%d%c", &hardness, &check) != 2 || check != '\n') && clean_stdin()) || hardness < 1 || hardness > 3);


    // convert hardness to in game top numbers for var1 & var2
    hardness = (hardness +1) * 5 +1;

    // delay for animation sake
    usleep(800000);
    clear();

    // game loop when score is less than 15
    while(score < 15)
    {
        // user input reset
        input = 0;

        // pseudo random numbers generator, using system time as seed
        srand48(time(NULL) % 257);
        var1 = drand48() * 10000;
        var1 = var1 % hardness;
        srand48(time(NULL));
        var2 = drand48() *257;
        var2 = var2 % hardness;

        // seed generator for opartion decision
        srand48(time(NULL) % 1234);
        seed = (drand48() *12345);
        seed = seed  % 100;

        // swap var1 and var2 if - opartions is generated and var2 > var1 to avoid negative numbers
        if(seed > 33 && seed <= 66 && var1 < var2)
        {
            var1 = var1 ^ var2;
            var2 = var1 ^ var2;
            var1 = var1 ^ var2;
        }

        // op for opartion printing and result sum for checking user answer
        op = opera(seed, var1, var2, &result);

        // recive answer from user
        do
        {
            clear();
            // score print
            showscore(score);

            // print exrcise
            printf("\n%i %c %i = ", var1, op, var2);
        }
        while((scanf("%d%c", &input, &check) !=2 || check != '\n') && clean_stdin());

        // cheat
        if(input == 257)
            break;

        // clear screen for animation sake
        clear();

        // check for right answer
        if(input == result)
        {
            // score update and right answer counter update
            score++;
            rac++;

            // print score and right answer massage
            showscore(score);
            printf("\n%i is Correct! +1 Point!\n", result);

            // delay for animation sake
            usleep(1200000);
        }

        // wrong answer handle
        else
        {
            // wrong answer counter update
            wac++;

            // 0 or 1 score handle (to avoid negate score)
            if(score == 0 || score == 1)
            {
                score = 0;
                showscore(score);
                printf("\n%i is Wrong!", input);
            }

            // 1 > score handle
            else
            {
                // score update
                score-=2;

                // score print wrong answer massage
                showscore(score);
                printf("\n%i is Wrong! -2 Points!", input);
            }

            // right answer print
            printf("\n\nThe Right answer is: %i\n\n", result);

            // delay for animation sake
            usleep(2000000);
        }

        // clear screen for animation sake
        clear();
    }

    // winning message
    for(int i = 0; i < 6; i++)
    {
        clear();
        usleep(400000);
        printf("########    VICTORY!!   ########\n\nRight answers: %i       Wrong answers: %i\n", rac, wac);
        printf("            Well Done!\n    Your'e great at 2nd Grade Math!\n");
        usleep(600000);
    }

    // delay for animation sake
    usleep(2500000);

    // program exit
    return 0;
}

void clear (void)
{
    // clear the screen
    printf("\033[2J");
    printf("\033[%d;%dH", 0, 0);
}

int clean_stdin (void)
{
    while(getchar() != '\n');
    return 1;
}

void showscore (score)
{
    // print score - usage at the begining of every turn during the game
    printf("score: %i points\n", score);
}

char opera (int seed, int var1, int var2, int* presult)
// this function return a relevant mathmetical opartion acording to the generated seed
{
    if(seed <= 33)
    {
        *presult = var1 * var2;
        return 'X';
    }
    else if(seed > 33 && seed < 66)
    {
        *presult = var1 - var2;
        return '-';
    }
    else
    {
        *presult = var1 + var2;
        return '+';
    }
}