Thread: C calculating program some help please!

I have made a simple calculating program. And I want some help on this. Well, I just want to improve this program.
I want a password protection and the timer.
And little advice could help.
Thank you.

Here's the code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <conio.h>
#include <string.h>


void load_menu(void);
void sum(void);
void sum3(void);
void product(void);
void product3(void);
void division(void);
void difference(void);
void difference3(void);
void square_root(void);
void percentage(void);
void FileCopying(void);
void CharacterCounting(void);
void Guess(void);
void rest(void);



int main(int argc, char** argv)
{
int ch;



printf("****WELCOME TO MY CALCULATING PROGRAM(includes some random stuff)!!****");
printf("\n\nPress ENTER to continue.");

while ((ch = getchar()) != '\n' && ch != EOF)
;
printf("\nLOADING.........");
while ((ch = getchar()) != '\n' && ch != EOF)
;
system("cls");
load_menu();

return 0;
}

void load_menu(void)
{
int choice;

do
{
printf("\t*******Menu*******\n\n");
printf("\t1. Sum\n");
printf("\t2. Sum of Three Integers\n");
printf("\t3. Product\n");
printf("\t4. Product of Three Integers\n");
printf("\t5. Division\n");
printf("\t6. Difference\n");
printf("\t7. Difference of Three Integers\n");
printf("\t8. Square Root of the Number\n");
printf("\t9. Percentage\n");
printf("\t10. File Copying\n");
printf("\t11. Character Counting\n");
printf("\t12. Rest\n");
printf("\t13. Exit(Bad choice)\n");
printf("\t\n\nChoose one you want to try.\n");
scanf_s("%d", &choice);

switch (choice)
{
case 1: sum();
break;
case 2: sum3();
break;
case 3: product();
break;
case 4: product3();
break;
case 5: division();
break;
case 6: difference();
break;
case 7: difference3();
break;
case 8: square_root();
break;
case 9: percentage();
break;
case 10: FileCopying();
break;
case 11: CharacterCounting();
break;
case 12: rest();
break;
case 13: printf(":( WE hope you come back soon! Press ENTER to quit. \n");
system("PAUSE");
exit(0);

default: printf("Invalid choice: Please enter the number that is IN the menu! \n");
system("PAUSE");
system("cls"); 
break;
}

} while (choice != 13);

}

void sum(void)
{
int num1, num2;
int ch;

printf("Enter number 1: ");
scanf_s("%d", &num1);
printf("Enter number 2: ");
scanf_s("%d", &num2);

printf("\nThe sum of the numbers was: %d", num1 + num2);


while ((ch = getchar()) != '\n' && ch != EOF);

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;
}

void sum3(void)
{
int num1, num2, num3;
int ch;

printf("Enter number 1:");
scanf_s("%d", &num1);
printf("Enter number 2:");
scanf_s("%d", &num2);
printf("Enter number 3:");
scanf_s("%d", &num3);

printf("\nThe sum of the numbers was: %d", num1 + num2 + num3);


while ((ch = getchar()) != '\n' && ch != EOF);

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;

}

void product(void)
{
int num1, num2;
int ch;

printf("Enter number 1: ");
scanf_s("%d", &num1);
printf("Enter number 2: ");
scanf_s("%d", &num2);

printf("\nThe product of the numbers was: %d", num1 * num2);

while ((ch = getchar()) != '\n' && ch != EOF);

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;
}

void product3(void)
{
int num1, num2, num3;
int ch;

printf("Enter number 1: ");
scanf_s("%d", &num1);
printf("Enter number 2: ");
scanf_s("%d", &num2);
printf("Enter number 3: ");
scanf_s("%d", &num3);

printf("\nThe product of the numbers was: %d", num1 * num2 * num3);

while ((ch = getchar()) != '\n' && ch != EOF)

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;

}

void division(void)
{
float num1, num2; // fix this part 
int ch;

printf("Enter a number 1: ");
scanf_s("%f", &num1);
printf("Enter a number 2: ");
scanf_s("%f", &num2);

printf("\nThe quotient of the numbers was: %f", num1 / num2); 

while ((ch = getchar()) != '\n' && ch != EOF)

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;

}

void difference(void)
{
int num1, num2;
int ch;

printf("Enter a number 1: ");
scanf_s("%d", &num1);
printf("Enter a number 2: ");
scanf_s("%d", &num2);

printf("\nThe difference of the numbers was: %d", num1 - num2);

while ((ch = getchar()) != '\n' && ch != EOF);

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;
}

void difference3(void)
{
int num1, num2, num3;
int ch;

printf("Enter number 1: ");
scanf_s("%d", &num1);
printf("Enter number 2: ");
scanf_s("%d", &num2);
printf("Enter number 3: ");
scanf_s("%d", &num3);

printf("\nThe product of the numbers was: %d", num1 - num2 - num3);

while ((ch = getchar()) != '\n' && ch != EOF)

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;

}

void square_root(void)
{
float num;
int ch;

printf("Enter a number that you want to take a square root: ");
scanf_s("%f", &num);

printf("\nThe square root of the number was: %f", sqrt(num));

while ((ch = getchar()) != '\n' && ch != EOF)

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;


}

void percentage(void)
{
int inp;
float c, ch;

printf("Type the percentage:");
scanf_s("%f", &ch);
printf("\nThe number that will take the percentage: ");
scanf_s("%f", &c);

printf("\nThe percent of the number is: %f", ((0.01)*ch)*c);

while ((inp = getchar()) != '\n' && inp != EOF)

printf("\n\nPress ENTER to continue.");
while ((inp = getchar()) != '\n' && inp != EOF)
;

system("PAUSE");
system("cls");
return;

}
void FileCopying(void)
{
int c, ch;


printf("Type the character you want to copy. \n");
printf("On Windows, ctrl+z for EOF and press ENTER and it goes back. \n");

c = getchar();
while (c != EOF) {
putchar(c);
c = getchar();
}

while ((ch = getchar()) != '\n' && ch != EOF);

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("PAUSE");
system("cls");
return; 
}

void CharacterCounting(void)
{
long nc;
int ch;

printf("This is the character counting part.\n");
printf("Press CTRL + Z for EOF signal. After you're done typing some characters.\n");

nc = 0;
while (getchar() != EOF)
++nc;
printf("%ld\n", nc);

while ((ch = getchar()) != '\n' && ch != EOF);

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;




system("PAUSE");
system("cls");
return;

}



void rest(void)
{
int ch;

printf("Sleepy sleepy... zZZzZzZz\n");
printf("You now feel awake again!\n");


while ((ch = getchar()) != '\n' && ch != EOF);

printf("\n\nPress ENTER to continue.");
while ((ch = getchar()) != '\n' && ch != EOF)
;

system("cls");
return;
}

Thank you, that was helpful!