C++ Simple 0-10 multiplication flashcard using rand()

Question

I am having trouble grasping the concept of rand() and srand() in c++. I need to create a program that displays two random numbers, have the user enter a response, then match the response with a message and do this for 5 times.

My question is how do I use it, the instructions say I can't use the time() function and that seems to be in every tutorial online about rand().

this is what I have so far.

#include <iostream>
#include <cmath>
#include <cstdlib>

using namespace std;

int main()
{

int seed;
int response;

srand(1969);
seed=(rand()%10+1);

cout<<seed<<" * "<<seed<<" = ";
cin>>response;
cout<<response;
    if(response==seed*seed)
    cout<<"Correct!. you have correctly answered 1 out of 1."<<endl;
    else 
    cout<<"Wrong!. You have correctly answered 0 out of 1."<<endl;

This just outputs something like 6*6 or 7*7, I thought the seed variable would be not necessary different but not the same all the time?

This is what the output should look like:

3 * 5 =
34
Wrongo. You have correctly answered 0 out of 1.
8 * 1 =
23
Wrongo. You have correctly answered 0 out of 2.
7 * 1 =
7
Correct! You have correctly answered 1 out of 3.
2 * 0 =
2
Wrongo. You have correctly answered 1 out of 4.
8 * 1 =
8
Correct! You have correctly answered 2 out of 5.

Final Results: You have correctly answered 2 out of 5 for a 40% average.

and these are the requirements:

Your program should use rand() to generate pseudo-random numbers as needed. You may use srand() to initialize the random number generator, but please do not use any 'automatic' initializer (such as the time() function), as those are likely to be platform dependent. Your program should not use any loops.

Well since you can not seed the rand() with a time can you ask the user to enter a number and use that as a seed or similar? — drescherjm, Sep 09 '12 at 23:45
**don't use `srand()` and `rand()` in C++**. Use ``, see oldrinb's answer. — Walter, Oct 31 '13 at 11:20

score 2 · Answer 1 · answered Sep 10 '12 at 00:07

By the way, since this is C++, you should really seek to use std::uniform_int_distribution, e.g.

#include <functional>
#include <random>
...
auto rand = std::bind(std::uniform_int_distribution<unsigned>(0, 10),
    std::default_random_engine());

Now, you can just use rand() to generate a number in the desired interval.

Jesse Good · Accepted Answer · 2012-09-10T00:25:30.543

The way you are using it now seems fine. The reason why all the tutorials use time() is because the numbers will be different every time you run your program. So, if you use a fixed number, every time your program runs, the output (number generation) will be the same. However, according to your requirements this doesn't seem to be a problem (if you need the random generation to be different every time you run your program, please specify that in your question).

However, rand()%10+1 is a range from 1 to 10 and not 0 to 10 like you want.

AFTER EDITS

To get the desired output, all you need is to make two seeds like so:

seed1=(rand()%11);
seed2=(rand()%11);
cout<<seed1<<" * "<<seed2<<" = ";

Also, you can ask the user for a seed and then pass that to srand to make each run more random.

About the requirements:

please do not use any 'automatic' initializer (such as the time() function), as those are likely to be platform dependent

std::time is a standard C++ function in the <ctime> header. I do not understand why it matters if the result is platform dependent.

Your program should not use any loops.

This is also a very strange requirement. Loops are fundamental building blocks of any program. The requirements seem very strange to me, I would ask your professor or teacher for clarification.

@SaniHuttunen: Yes, that is true. However, the number is only predictable if you run the program more than once. Perhaps that is what the OP wants, but the problem description does not specify this. — Jesse Good, Sep 09 '12 at 23:53
Well... to me "two random numbers" suggests that the numbers should be (pseudo) random with each run. But I might be mistaken. — Sani Huttunen, Sep 09 '12 at 23:55

Aesthete · Answer 3 · 2012-09-10T00:31:47.560

0

You use srand() to seed the random function. This is necessary otherwise you'd get the same sequence of number with each run, and each call to rand()

You can seed rand with whatever you please. You'll find most tutorials use the current time as a seed as the number returned is usually different with each run of the program.

If you truly can't use the time() functionality, I would pass the seed as a command line argument.

int main(int argc, char* argv[])
{
    srand(atoi(argv[1])); // Seed with command line argument.
}

edited Sep 10 '12 at 00:31

answered Sep 09 '12 at 23:24

Aesthete

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I've added my suggested solution. – Aesthete Sep 10 '12 at 00:32
If you know the seed then you can predict the numbers. This isn't random. – Sani Huttunen Sep 10 '12 at 10:40

score 0 · Answer 4 · edited May 23 '17 at 12:03

0

On windows you can use GetTickCount() instead if time().
You could use rand_s which doesn't need to be seeded.
On *nix systems you can utilize /dev/random.

(How to use /dev/random)

edited May 23 '17 at 12:03

Community

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answered Sep 09 '12 at 23:39

Sani Huttunen

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C++ Simple 0-10 multiplication flashcard using rand()

4 Answers4