multiplication game loop slide issue - c++

Question

So I am determined to make an epic math console based game for fun.
I am curious as to why when the random enters a zero, the program slides through a series of multiplied by 0 and skips the "please enter: " portion of my code.. Is this because of the true and false boolean features of the test condition in the while loop? More importantly how can I stop this from happening?
Thank you for all of your help!
// multiplicationgame.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
#include <stdlib.h>
#include <time.h>
using namespace std;
void game();
int _tmain(int argc, _TCHAR* argv[])
{
// waiting.cpp : Defines the entry point for the console application.
//
cout << "Welcome to Math game!\n\n" << endl;
float secs;
secs = 3;
clock_t delay = secs * CLOCKS_PER_SEC;
clock_t start = clock();
while (clock() - start < delay )
;
char choice = 'z';
game();
while(choice != 'n')
{
cin >> choice;
if (choice == 'y')
{
cout << "\n\n";
game();
}
else
choice = 'n';
}
return 0;
}
void game()
{
float secs;
secs = 33;
clock_t delay = secs * CLOCKS_PER_SEC;
clock_t start = clock();
int correct = 0;
while (clock() - start < delay )
{
srand(time(NULL));
int a = rand() % 23;
int b = rand() % 23;
int c = (a * b);
int d = 0;
char choice = 0;
cout <<"What does " << a << " * " << b << " equal?" << endl << endl << endl;
cout << "\n";
while(d != c)
{
cout << "Please enter a number: ";
cin >> d;
if(d == c)
++correct;
}
cout << "\n\nCorrect! " << (a * b) << " is the answer!" << endl << endl;
}
cout << "Your score is: " << correct << "\n\n" <<endl;
cout << "Would you like to play again (Y) or (N)?\n\n\n";
}

Answer 1

You assume the answer is wrong if c is not equal to d, but if a or b are set to zero , c and d are equal before your user can ever enter a number. One solution would be to use a do { ... } while ( ... ); loop instead of a while loop to ensure the user is always asked for a number before your test for the correct answer is performed.

Answer 2

As Markku said, don't set d = 0, because if either a or b is equal 0, then c = a * b = 0 and then your while loop condition c != d won't hold and so it will be skipped

Answer 3

You initialize d to be 0, and anything times 0 is 0. Thus the (d != c) condition will always be false, and you don't enter the while(d!=c) loop.
You are getting 0 several times, because the while loop finishes very quickly, and so when you call srand(time(NULL)), time(NULL) will return the same value as the previous itteration, and you get the same random seed (which gets you 0 again).
initialize d to be -1 (or some other value that a*b can't be). Move the srand outside of your while loop -- you only have to (and only should) call srand once in your program.
John

Answer 4

Quick fix: initialize int d = -1; instead of int d = 0;.
You're initializing int c = a * b. Since either a or b is zero, the multiplication results in c being zero. You also initialize int d = 0;. Then you have while(d != c), but you assigned both of them to zero, hence your program skips over that loop because d != c is false.

Answer 5

#AEGIS No, the srand(time(NULL)) merely seeds the random number generator with a somewhat random value based on the current time whenever the program is run. This ensures that each run of the program will produce a different set of multiplication problems to solve.
#AEGIS The outer while (clock() - start < delay ) { ... } loop terminates when the "delay" time has expired. The inner while(d != c) { ... } loop is never entered at all when a or b are zero, or loops forever as long as the user enters wrong answers. So though it is not a real problem in practice -- any user is likely to finally get the correct answer or abort the program manually -- this is a program which is not certain to ever terminate.
#Ned Nowonty looking at the screen shot AEGIS provided the outer loop didn't terminate. If it did then the
Your score is: (some number)
Would you like to play again (Y) or (N)?
would have appeared. When you srand with the same initializer you end up with the same pseudo random numbers. So when one of the variables was initialized to 0 it would loop around until time(NULL) provided srand a different variable. In order to avoid that you could use an iterator as well as the time function so the seed would be different all the time.