Help in a program

[2nick82]

How to generate 50 distinct numbers in an array?
I have the code for generating 50 numbers but thay are not different. I get same number sometimes twice or three time.
Here is my code:

#include <iostream>
#include <cstdlib>
#include <ctime>

using namespace std;

int num;
int main()
{
    int array[50];
    for(int i = 0; i<50; i++)
    {
        array[i] = rand()%99;
    }
    for(int i = 0; i<50; i++)
    {
        cout<<array[i]<<" ";
    }
      cout <<"\nEnter an integer between 0 & 99: ";
      cin >> num;
      int flag = 0;
     
           for(int k = 0; k < 50; k++)
      {
        if(array[k] == num)
        {
    cout << "Number found in array index " << k << "."
         << endl;
         flag += 1;
        }
      }
      if(flag < 1)
      {
        cout << "number not found." << endl;
      }
     return 0;
}

[Ravalon]

How to generate 50 distinct numbers in an array?
I have the code for generating 50 numbers but thay are not different. I get same number sometimes twice or three time.

That's normal. :) Random numbers aren't defined to not repeat. In fact, it's possible, but not probable, that you could randomly pick the same number infinitely. That's just how random numbers are, but a lot of people want a random shuffle instead of just a list of random numbers. :)

To make sure that the numbers don't repeat, you can fill an array in order with the numbers in your range and then shuffle it using rand() to pick the index to swap with. The easy way is to use the random_shuffle() function from <algorithm> because you don't have to think, but it's pretty simple to write your own too.

#include <algorithm>
#include <cstdlib>
#include <iostream>


namespace Raye {
  void randomShuffle( int a[], size_t n )
  {
    for ( int i = 0; i < n - 1; i++ ) {
      // Don't shuffle the parts that have already been shuffled
      std::swap( a[i], a[i + rand() % ( n - i )] );
    }
  }


  void display( const char *label, int a[], size_t n )
  {
    using namespace std;

    cout << label << "\n";
    for ( int i = 0; i < n; i++ )
      cout << a[i] << ' ';
    cout << '\n';
  }
}


int main()
{
  const int N = 20;

  int a[N];
  int b[N];
  int k = 50;

  // You can pick any numbers you want!
  for ( int i = 0; i < N; i++ )
    a[i] = b[i] = k++;

  // You should prefer random_shuffle()
  std::random_shuffle( a, a + N );
  Raye::randomShuffle( b, N );

  // Make sure that it worked :)
  Raye::display( "a:", a, N );
  Raye::display( "b:", b, N );

  return 0;
}

[2nick82]

Here is my problem:
A container that holds 50 distinct integers has two ends: top and bottom. When an input integer matches one of the integers in the container, it is then moved to the top, and all the integers above the matched integer are moved down to fill the gap in the container (keeping the same order). When none of the integers in the container matches the input value, the bottom integer is discarded, the remaining integers are moved down to fill the gap (keeping the same order), and the input integer is inserted on top.

I have to input an integer then compare it with the array of generated numbers.
Do u have any idea?
thanks for you reply

That's normal. :) Random numbers aren't defined to not repeat. In fact, it's possible, but not probable, that you could randomly pick the same number infinitely. That's just how random numbers are, but a lot of people want a random shuffle instead of just a list of random numbers. :)

To make sure that the numbers don't repeat, you can fill an array in order with the numbers in your range and then shuffle it using rand() to pick the index to swap with. The easy way is to use the random_shuffle() function from <algorithm> because you don't have to think, but it's pretty simple to write your own too.

#include <algorithm>
#include <cstdlib>
#include <iostream>


namespace Raye {
  void randomShuffle( int a[], size_t n )
  {
    for ( int i = 0; i < n - 1; i++ ) {
      // Don't shuffle the parts that have already been shuffled
      std::swap( a[i], a[i + rand() % ( n - i )] );
    }
  }


  void display( const char *label, int a[], size_t n )
  {
    using namespace std;

    cout << label << "\n";
    for ( int i = 0; i < n; i++ )
      cout << a[i] << ' ';
    cout << '\n';
  }
}


int main()
{
  const int N = 20;

  int a[N];
  int b[N];
  int k = 50;

  // You can pick any numbers you want!
  for ( int i = 0; i < N; i++ )
    a[i] = b[i] = k++;

  // You should prefer random_shuffle()
  std::random_shuffle( a, a + N );
  Raye::randomShuffle( b, N );

  // Make sure that it worked :)
  Raye::display( "a:", a, N );
  Raye::display( "b:", b, N );

  return 0;
}

[Ravalon]

Here is my problem:
A container that holds 50 distinct integers has two ends: top and bottom. When an input integer matches one of the integers in the container, it is then moved to the top, and all the integers above the matched integer are moved down to fill the gap in the container (keeping the same order). When none of the integers in the container matches the input value, the bottom integer is discarded, the remaining integers are moved down to fill the gap (keeping the same order), and the input integer is inserted on top.

That's a priority queue. :) The big operation with this one is the array shift. It's not very efficient, but you need to copy all of the cells from 0 to n - 2 into the cells 1 to n - 1. That overwrites the last cell and leaves a hole in the first cell for whatever value needs to go there. A function to do that is really simple once you know how it works. :)

int shiftRight( int a[], int n )
{
  // Save the cell we're going to lose
  int last = a[n - 1];

  // Copy over the right cell using the left
  // from right to left in the array
  for ( int i = n - 1; i > 0; i-- )
    a[i] = a[i - 1];

  return last;
}

But that only works for the last cell. I don't want to take the eductional aspect away by doing your work for you, but it's not too hard to turn shiftRight() into a function that returns a and only shifts from 0 to i. I'll leave that as an exercise for you. After you get shiftRight() working the way you want, the rest of the program is a breeze. :)