在数组C ++中生成唯一随机数

Question

I have coded an array with 3 random integers inside of it. The key is though that I want the 3 random integers to be different than each other (unique random numbers). My problem is that even when the numbers are unique, I still get a 'bad' reading from them. I seeded my random numbers with time(NULL) and because of this I put a Sleep(x) function in between each declaration to increase variety in numbers. The following code is all of my code inside my main() function. For testing purposes, I didn't include a break statement in my code so I could test the program over and over.

srand((unsigned)time(NULL));

while(true)
{
    //Generate 3 numbers
    int a = rand() % 7 + 1;
    Sleep(1000);
    int b = rand() % 8 + 1;
    Sleep(1000);
    int c = rand() % 9 + 1;
    int array[3] = { a , b , c };

    //Check the numbers to make sure none of them equal each other
    if( (array[a] == array[b]) || (array[a] == array[c]) || (array[b] == array[c]) )
    {
        //Print all numbers
        for(int x = 0; x < 3; x++)
            cout << array[x] << endl;
        cout << "bad" << endl;
        system("pause");
        system("cls");
    }
    else
    {
        //Print all numbers
        for(int x = 0; x < 3; x++)
            cout << array[x] << endl;
        cout << "good" << endl;
        system("pause");
        system("cls");
    }   
}
system("pause");
return 0;   

Answer 1

The problem with the current check is it checks at the indices represented by the random values, and not the random values themselves, which are the first 3 elements.

Simply replace

if( (array[a] == array[b]) || (array[a] == array[c]) || (array[b] == array[c]) )

with

if( (array[0] == array[1]) || (array[0] == array[2]) || (array[1] == array[2]) )

or just

if(a == b || a == c || b == c)

Answer 2

It appears you're using Sleep , a Windows-specific function that has nothing to do with the C library. srand affects the sequence returned by rand() which is repeatable if srand() is given the same seed.

Secondly, the range of random numbers that you are storing in a , b and c can possibly cause out of bounds array access in this line here:

if( (array[a] == array[b]) || (array[a] == array[c]) || (array[b] == array[c]) )

array only has 3 elements, yet the values in a , b and c can be higher than that.

Since you are using C++, consider taking advantage of the C++ standard library.

First create a vector of a specified size, and use std::iota to fill it with values in the range [0, 10).

std::vector<int> v(10);
std::iota(v.begin(), v.end(), 0);

Then we use std::random_shuffle to reorder the values.

std::random_shuffle (v.begin(), v.end());

And pick the top three values:

for (int i = 0; i < 3; ++i)
    std::cout << v[i] << " ";

Answer 3

1. Like everyone else said, the sleeps don't do anything.
2. The shuffle idea isn't great. Its slower than regenerating the numbers until you get unique ones, and it doesn't scale very well. If you wanted your range of allowed numbers to be large the shuffle would become prohibitively expensive.

I would do something like this:

int a = rand() % 7 + 1;

int b = rand() % 8 + 1;
while( a == b ) 
   b = rand() % 8 + 1;

int c = rand() % 9 + 1;
while(( a == c ) || ( b == c )) 
   c = rand() % 9 + 1;

int array[3] = { a , b , c };

3. Your check for "bad values" should be:

   if ( ( a == b) || ( a == c ) || ( b == c ) )