CODEWITHSUNDEEP
c++
user466534
user466534

Reputation:

random shuffle operation

i have following code

#include <iostream>
#include <cstdlib>
using namespace std;


int main()
{    
    int a[] = {2, 1, 4, 3, 5, 6, 7, 9, 8, 10, 11};
    int n = sizeof(a) / sizeof(int);
    int k=0;

    for (int i = 0; i < n; i++)
    {
        k = i + rand() % (n-1-i);
        int s = a[i];
        a[i] = a[k];
        a[k] = s;     
    }

    for (int i = 0; i < n; i++)
    {     
        cout << a[i] << "  " << endl;
    }

    return 0;
}

but it gives me runtime error,i know there is a lot of method in internet ,just i choose such simple for exam preparation in university,please help me what is wrong?

Upvotes: 0

Views: 297

Answers (3)

Philip
Philip

Reputation: 1551

n = 11. When i = 10, that's a k= i+rand() % 0;

Mod by zero is undefined and can operate a number of different ways. I've seen it equivalent to mod infinity, so it would be returning k as i+rand() which would lead to your out-of-bounds error.

Upvotes: 0

Mark Ransom
Mark Ransom

Reputation: 308121

You might want to ask yourself what the result of %(n-1-i) will be for all possible values of i.

Upvotes: 1

Fred Larson
Fred Larson

Reputation: 62053

I think rand()%(n-1-i) will give you a divide-by-zero for certain values if i (like i == n-1).

Upvotes: 1

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