OK, this is a one-time deal only, post any more huge masses of code without formatting and I'll delete it until you get it right.
Plus we have better things to do that wade through masses of code. Pick a small example which focusses on your specific question. A thousand lines of non-portable poorly formatted code with "please fix it for me" is no way to go.

Here is your code formatted - nothing more, nothing less. I'm not going to say what's wrong for the moment because I don't have the time.
Code:
#include <stdio.h>
#include <conio.h>
#include <dos.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

// GLOBAL VARIABLES
//**************************************************  ****************************
int num_easy, num_medium, num_hard, num_easy2, num_medium2, num_hard2,
    point;
char x, y;
FILE *score;
char menu;
char login[100], name[100], data[100];
//**************************************************  ****************************



// PROTOTYPE FUNCTIONS
//**************************************************  ****************************
int random_easy(void);
int random_easy2(void);
int random_medium(void);
int random_medium2(void);
int random_hard(void);
int random_hard2(void);
int campur(int num1, int num2);
int tolak(int num1, int num2);

int darab(int num1, int num2);
float bahagi(float num1, float num2);
float round(float f);
void operasi(void);
void start_game_easy(void);
void start_game_medium(void);
void start_game_hard(void);
void menu_level(void);
void operasi(void);
void scoreboard();
void play();
void mainmenu();
void robot(void);
void robot2(void);
void robot3(void);
void robot4(void);
void animation(void);
//**************************************************  ****************************



// LOGIN
//**************************************************  ****************************
void log()
{
    textcolor(RED);
    puts("\n\n\n\n");
    printf("\t");
    cprintf
        ("**************************************************  ************");
    printf("\t\t\t\t\t");
    cprintf("Welcome to the MATHGAME!");
    printf("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************\n");
    puts("\n\n\n\t\t\tPlease enter your name");
    printf("\n\t\t\t>> ");
    gets(login);
}

//**************************************************  ****************************


// MAIN FUNCTION
//**************************************************  ****************************
void main()
{
    animation();
    log();
    mainmenu();
}

//**************************************************  ****************************



// MAIN MENU
//**************************************************  ****************************
void mainmenu()
{
  menu:
    clrscr();
    textcolor(RED);
    puts("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************");
    printf("\t\t\t\t\t\t");
    cprintf("MAIN MENU");
    printf("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************\n");
    printf("\n\t\t\tWelcome %s !", login);
    score = fopen("data.txt", "r+");

    while (!feof(score)) {
        fscanf(score, "%s", &name);
        if (strcmp(login, name) == 0) {
            fscanf(score, "%d", &point);
            printf("\n\t\t\tYour previous point was %d.", point);
            break;
        }
        if (feof(score))
            puts("\n\t\t\t<<Welcome, new player!>>");

    }
    puts("\n\n\n\t\t\t1. START GAME!");
    puts("\t\t\t2. Scoreboard");
    puts("\t\t\t3. Quit\n");
    printf("\n\n\t\t    Please enter selection... ");
  choose:
    menu = getch();

    switch (menu) {
    case '1':
        operasi();
        break;
    case '2':
        scoreboard();
        break;
    case '3':{
            puts("\n\n\n\n\t\t\t<< Game ended >>");
            sleep(1);
            exit(1);
        }

    default:
        goto choose;
    }
    getch();
}

//**************************************************  ****************************



// RANDOMIZING EASY QUESTIONS
//**************************************************  ****************************
int random_easy(void)
{
    randomize();
    num_easy = rand() % 10;
    return (num_easy);
}

int random_easy2(void)
{
    randomize();
    num_easy2 = random(10);
    return (num_easy2);
}

//**************************************************  ****************************



// RANDOMIZING MEDIUM QUESTIONS
//**************************************************  ****************************
int random_medium(void)
{

    randomize();
    num_medium = random(100) % 100;
    if (num_medium < 10)
        num_medium += 10;
    return (num_medium);
}

int random_medium2(void)
{

    randomize();
    num_medium2 = rand() % 100;
    if (num_medium2 < 10)
        num_medium2 += 10;
    return (num_medium2);
}

//**************************************************  ****************************



// RANDOMIZING HARD QUESTIONS
//**************************************************  ****************************
int random_hard(void)
{

    randomize();
    num_hard = rand() % 1000;
    if (num_hard < 100)
        num_hard += 100;
    return (num_hard);
}

int random_hard2(void)
{
    randomize();
    num_hard2 = random(1000);
    if (num_hard2 < 100)
        num_hard2 += 100;

    return (num_hard2);
}

//**************************************************  ****************************



// ADDITION
//**************************************************  ****************************
int campur(int num1, int num2)
{
    int jumlah;
    if (x == '1') {
        num1 = random_easy();
        num2 = random_easy2();
    } else if (x == '2') {
        num1 = random_medium();
        num2 = random_medium2();
    } else if (x == '3') {
        num1 = random_hard();
        num2 = random_hard2();
    }

    printf(" %d + %d", num1, num2);
    jumlah = num1 + num2;

    return (jumlah);
}

//**************************************************  ****************************



// SUBSTRACTION
//**************************************************  ****************************
int tolak(int num1, int num2)
{
    int jumlah;
    if (x == '1') {
        num1 = random_easy();
        num2 = random_easy2();
    } else if (x == '2') {
        num1 = random_medium();
        num2 = random_medium2();
    } else if (x == '3') {
        num1 = random_hard();
        num2 = random_hard2();
    }
    printf(" %d - %d", num1, num2);
    jumlah = num1 - num2;

    return (jumlah);
}

//**************************************************  ****************************



// MULTIPLICATION
//**************************************************  ****************************
int darab(int num1, int num2)
{
    int jumlah;
    if (x == '1') {
        num1 = random_easy();
        num2 = random_easy2();
    } else if (x == '2') {
        num1 = random_medium();
        num2 = random_medium2();
    } else if (x == '3') {
        num1 = random_hard();
        num2 = random_hard2();
    }
    printf(" %d x %d", num1, num2);
    jumlah = num1 * num2;

    return (jumlah);
}

//**************************************************  ****************************



// DIVISION
//**************************************************  ****************************
float bahagi(float num1, float num2)
{
    float jumlah;
    if (x == '1') {
        num1 = random_easy();
        num2 = random_easy2();
    } else if (x == '2') {
        num1 = random_medium();
        num2 = random_medium2();
    } else if (x == '3') {
        num1 = random_hard();
        num2 = random_hard2();
    }
    printf(" %.0f / %.0f", num1, num2);
    jumlah = num1 / num2;
    jumlah = round(jumlah * 100) / 100;
    return (jumlah);
}

//**************************************************  ****************************



// STARTING EASY GAME
//**************************************************  ****************************
void start_game_easy(void)
{
    clrscr();
    int n = 1;
    float jumlah_game_easy;
    float answer;
    while (n <= 10) {
        clrscr();
        textcolor(RED);
        puts("\n");
        printf("\t");
        cprintf
            ("**************************************************  ************");
        printf("\t\t\t\t\t\t");
        if (y == '1')
            printf("ADD IT UP: ");
        else if (y == '2')
            printf("MINUS IT: ");
        else if (y == '3')
            printf("TIMES IT: ");
        else if (y == '4')
            printf("DIVIDE IT: ");
        printf("Peanut!");
        printf("\n");
        printf("\t");
        cprintf
            ("**************************************************  ************\n");
        printf("\n\n\tAnswer these 10 questions..");
        printf("\n\n\n\tTry question no. %d :\n", n);
        puts("\t\t\t\t--------");
        printf("\t\t\t\t");
        if (y == '1')
            jumlah_game_easy = campur(num_easy, num_easy2);
        else if (y == '2')
            jumlah_game_easy = tolak(num_easy, num_easy2);
        else if (y == '3')
            jumlah_game_easy = darab(num_easy, num_easy2);
        else if (y == '4')
            jumlah_game_easy = bahagi(num_easy, num_easy2);
        puts("\n\t\t\t\t--------");
        if (y == '4')
            puts("\n\tHint:Give you answer in two decimal places");
        printf("\n\n\tYour answer >> ");
        scanf("%f", &answer);
        if (answer == jumlah_game_easy) {
            printf("\n\n\tWELL DONE!\n\t10 points for you!");
            point += 10;
            sleep(1);
        } else if (answer != jumlah_game_easy) {
            printf("\n\tNope, wrong answer!");
            sleep(1);
        }
        n++;
    }
    printf("\n\n\t<<Your total point is %d>>", point);
    score = fopen("data.txt", "r+");
    fprintf(score, "%s %d", login, point);
    play();
}

//**************************************************  ****************************



// STARTING MEDIUM GAME
//**************************************************  ****************************
void start_game_medium(void)
{
    clrscr();
    int n = 1;
    float answer;
    float jumlah_game_medium;
    while (n <= 10) {
        clrscr();
        textcolor(RED);
        puts("\n");
        printf("\t");
        cprintf
            ("**************************************************  ************");
        printf("\t\t\t\t\t\t");
        if (y == '1')
            printf("ADD IT UP: ");
        else if (y == '2')
            printf("MINUS IT: ");
        else if (y == '3')
            printf("TIMES IT: ");
        else if (y == '4')
            printf("DIVIDE IT: ");
        printf("Piece of cake!");
        printf("\n");
        printf("\t");
        cprintf
            ("**************************************************  ************\n");
        printf("\n\n\tAnswer these 10 questions..");
        printf("\n\n\n\tTry question no. %d :\n", n);
        puts("\t\t\t\t---------");
        printf("\t\t\t\t");
        if (y == '1')
            jumlah_game_medium = campur(num_medium, num_medium2);
        else if (y == '2')
            jumlah_game_medium = tolak(num_medium, num_medium2);
        else if (y == '3')
            jumlah_game_medium = darab(num_medium, num_medium2);
        else if (y == '4')
            jumlah_game_medium = bahagi(num_medium, num_medium2);
        puts("\n\t\t\t\t---------");
        printf("\n\n\tYour answer >> ");
        scanf("%f", &answer);
        if (answer == jumlah_game_medium) {
            printf("\n\n\tWELL DONE!\n\t20 points for you!");
            point += 20;
            sleep(1);
        } else if (answer != jumlah_game_medium) {
            printf("\n\tNope, wrong answer!");
            sleep(1);
        }
        n++;
    }
    printf("\n\n\t<<Your total point is %d>>", point);
    score = fopen("data.txt", "r+");
    fprintf(score, "%s %d", login, point);
    play();
}

//**************************************************  ****************************



// STARTING HARD GAME
//**************************************************  ****************************
void start_game_hard(void)
{
    clrscr();
    int n;
    float answer, jumlah_game_hard;
    for (n = 1; n <= 10; n++) {
        clrscr();
        textcolor(RED);
        puts("\n");
        printf("\t");
        cprintf
            ("**************************************************  ************");
        printf("\t\t\t\t\t\t");
        if (y == '1')
            printf("ADD IT UP: ");
        else if (y == '2')
            printf("MINUS IT: ");
        else if (y == '3')
            printf("TIMES IT: ");
        else if (y == '4')
            printf("DIVIDE IT: ");
        printf("Wow!");
        printf("\n");
        printf("\t");
        cprintf
            ("**************************************************  ************\n");
        printf("\n\n\tAnswer these 10 questions..");
        printf("\n\n\n\tTry question no. %d :\n", n);
        puts("\t\t\t\t-----------");
        printf("\t\t\t\t");
        if (y == '1')
            jumlah_game_hard = campur(num_hard, num_hard2);
        else if (y == '2')
            jumlah_game_hard = tolak(num_hard, num_hard2);
        else if (y == '3')
            jumlah_game_hard = darab(num_hard, num_hard2);
        else if (y == '4')
            jumlah_game_hard = bahagi(num_hard, num_hard2);
        puts("\n\t\t\t\t-----------");
        printf("\n\n\tYour answer >> ");
        scanf("%f", &answer);
        if (answer == jumlah_game_hard) {
            printf("\n\n\tWELL DONE!\n\t20 points for you!");
            point += 20;
            sleep(1);
        } else if (answer != jumlah_game_hard) {
            printf("\n\tNope, wrong answer!");
            sleep(1);
        }
    }
    printf("\n\n\t<<Your total point is %d>>", point);
    score = fopen("data.txt", "r+");
    fprintf(score, "%s %d", login, point);
    play();
}

//**************************************************  ****************************



// CHOOSE LEVEL
//**************************************************  ****************************
void menu_level(void)
{
    clrscr();
    textcolor(RED);
    puts("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************");
    printf("\t\t\t\t\t\t");
    cprintf("GAME MENU");
    printf("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************\n");
    puts("\n\n\t\t    Please select level... ");
    puts("\n\n\t\t\t1. Easy");
    puts("\t\t\t2. Medium ");
    puts("\t\t\t3. Difficult ");
    puts("\n\t\t\t4. Back to Main Menu\n");
    printf("\t\t\t");
    printf("\n\n\t\t   Selection:");
  repeat:
    x = getch();

    switch (x) {
    case '1':
        start_game_easy();
    case '2':
        start_game_medium();
    case '3':
        start_game_hard();
    case '4':
        operasi();
    default:
        goto repeat;
    }

}

//**************************************************  ****************************



// CHOOSE OPERATION
//**************************************************  ****************************
void operasi(void)
{
    clrscr();
  repeat:
    textcolor(RED);
    puts("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************");
    printf("\t\t\t\t\t\t");
    cprintf("GAME MENU");
    printf("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************\n");
    puts("\n\n\t\t    Please select operation... ");
    puts("\n\n\t\t\t1. Addition +");
    puts("\t\t\t2. Substraction -");
    puts("\t\t\t3. Multiplication X");
    puts("\t\t\t4. Division /\n");
    puts("\t\t\t5. Back to Main Menu");
    printf("\n\n\t\t   Selection:");

  game:
    y = getch();

    switch (y) {
    case '1':
        break;
    case '2':
        break;
    case '3':
        break;
    case '4':
        break;
    case '5':
        mainmenu();
    default:
        goto game;
    }
    menu_level();
}

//**************************************************  ****************************



// VIEW SCOREBOARD
//**************************************************  ****************************
void scoreboard()
{
    char data[100];
    clrscr();
    textcolor(RED);
    puts("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************");
    printf("\t\t\t\t\t\t");
    cprintf("SCOREBOARD");
    printf("\n");
    printf("\t");
    cprintf
        ("**************************************************  ************\n");

    score = fopen("data.txt", "r+");

    if ((score = fopen("data.txt", "r+")) == NULL) {
        puts("\n\n\n\n\t\t\tError in reading database..");
        puts("\n\n\n\t\t\tReturning to Main Menu..");
        sleep(2);
        clrscr();
        return;
    }

    puts("\n");
    puts("\t\tNAME\t\t\tSCORE\n");

    while (!feof(score)) {
        fscanf(score, "%s", &data);
        printf("\t\t%s", data);
        fscanf(score, "%s", &data);
        printf("\t\t\t%s\n", data);
    }
    puts("\n\n\n\n\n\tPress any key to return to Main Menu..");
    getch();
    clrscr();
    mainmenu();
}

//**************************************************  ****************************



// PLAY AGAIN?
//**************************************************  ****************************
// Query to play again?

void play()
{
    char again;
    printf("\n\n\tPlay again? (Y/N)");
  playagain:
    again = getch();

    if ((again == 'Y') | (again == 'y'))
        operasi();
    else if ((again == 'N') | (again == 'n')) {
        clrscr();
        puts("\n\n\n\n\n\n\n\tThank you for playing!");
        puts("\tHave a Nice Day!\n\n");
        sleep(2);
        exit(1);
    } else
        goto playagain;

}

//**************************************************  ****************************

//ROUNDING UP THE NUMBERS
//**************************************************  ****************************

float round(float f)
{
    return floor(f + 0.5);
}

//**************************************************  ****************************



//animation
//**************************************************  ****************************

void animation(void)
{
    robot();
    sleep(3);
    clrscr();
    robot2();
    sleep(3);
    clrscr();
    robot3();
    sleep(3);
    clrscr();
    robot4();
    clrscr();
}


void robot(void)
{
    // snipped due
    printf("\n\n");
}

void robot2(void)
{
    // to them being
    printf("\n\n");
}

void robot3(void)
{
    // unrelated to the problems at hand
    printf("\n\n");
}

void robot4(void)
{
    printf("\n\n");
    sleep(2);
    printf("\t\t\t      Please wait.\n");
    printf("\t\t\t\tLoading");
    for (int j = 0; j < 2; j++) {
        clreol();
        sleep(1);
        for (int i = 0; i < 3; i++) {
            printf(".");
            sleep(1);
        }
        printf("\b\b\b");
    }
}