CODEWITHSUNDEEP
crandom
Genny Saxo
Genny Saxo

Reputation: 35

Unique random numbers

I have been working on a random number gen, that creates 6 unique random numbers 1-49, i can get it working so theres 6 random numbers 1-49, or 6 unique random numbers but not all of the above at the same time. I can get the code to compile but it just crashes everytime i try and use the % 49 +1 in different spots.

Code i am using is:

{
                int numbers [SIZE];
                int i, j, n;

                srand (time(NULL));

                for (i = 0; i < SIZE; i++)
                    numbers[i] = i;

                for(i = 0; i < SIZE; i++)
                {
                j = rand() % 49 + 1;
                n = numbers[j];
                numbers[j] = numbers[i];
                numbers[i] = n;
                }

                for (i = 0; i < SIZE; i++)
                MyOutputDebugString ("%d\n", numbers[i]);

SIZE is defined as 6.

Thanks

Upvotes: 0

Views: 321

Answers (2)

ixron
ixron

Reputation: 127

The error is comming from calling a portion of the array that does not exist. 

n = numbers[j];

The value for j is going to be your random number and most likly larger then your SIZE.

Change this part of your code:

                for (i = 0; i < SIZE; i++)                           
                    numbers[i] = i;

                for(i = 0; i < SIZE; i++)
                   {                       
                   j = rand() % 49 + 1; 
                   n = numbers[j];  
                   numbers[j] = numbers[i];
                   numbers[i] = n;
                   }

You can manage to pull off the same effect in one loop like this:

for (i = 0; 1 < SIZE; i++)
{
   numbers[i] = rand() % 49 + 1;
}

I hope this helps.

Upvotes: 0

Kiril Kirov
Kiril Kirov

Reputation: 38163

SIZE is defined as 6.

So, your array numbers is like

int numbers [6];

Once 

j = rand() % 49 + 1;

is executed, j will be between in [ 1; 49 ], so, if it's > 5, on this line, you'll have an out of range index::

n = numbers[j];

Upvotes: 5

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