Arrays

[markusfurst]

Hello,
I'm learning about arrays in c++ and have two questions. I have created this program that's randomizing numbers between 1-100, but somehow the last output number is always 0. And the second thing, now the output is just one long column with one empty line between each number(as I want) but what if I want to change it so all the 1:s is on one row, all the 2:s is on one row etc...

#include <iostream>
#include <iomanip>
#include <ctime>

using namespace std;

int main()
{
    const size_t SIZE = 300;
    int x[SIZE];
    int num;
    int i;
    
    cout << " How many integers do you want to randomize (<=300): ";
    cin >> num;
    
    
    srand(time(NULL));
    for(size_t idx=1; idx < num; idx++)
        x[idx] = (rand() % 100 + 1);
    

    for(i=1; i<=num; i++)
        cout << endl << x[i] << endl;
    
    return 0;
}

[lastchance]

markusfurst,

In C++ (but not in fortran) array indexing starts at 0. So the elements of x[] are
x[0], x[1], x[2], ... , x[299]
Both your for() loops need to be aware of this. On line 19 you should have idx=0 as initial value, not 1. On line 23 you should have 0 as initial value and use <num, not <=num.

If you want to have all the occurrences of a particular digit on one line then you will have to set up another array to count them.

[markusfurst]

@lastchance
Thank you!

How would I do that? Can you give me some more tips.

[AbstractionAnon]

As lastchance said, you need an array to count the occurrences.

  const int MAX_RAND = 100;
  int count[MAX_RAND+1] = {0};  // Here we ignore [0] and use [1]-[100] because of your rand() function.
...
//  Replace lines 19-20;
  int r;
  for(size_t idx=0; idx < num; idx++)
  {  r = rand() % MAX_RAND + 1;
      x[idx] = r;
      count[r]++;
  }

[lastchance]

I've limited the range of your random numbers to 0 - (RANGE-1), that is 0 - 9 by default below. Otherwise you will end up with an excessive proportion of blank lines.

Play around with the code and see what you get.

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

using namespace std;

int main()
{
   const int SIZE = 300;
   const int RANGE = 10;               // Limited range of random numbers to 0 - (RANGE-1)
   int x[SIZE];                                                                                                                      
   int count[RANGE] = { 0 };           // Initialises rest to zero, because I didn't specify all the initial values
   int numRandom;
   int r;
   int i, j;
    

   cout << " How many integers do you want to randomize ( <= " << SIZE << ": ";   cin >> numRandom;
   

   // Generate some random numbers
   srand( time(NULL ) );
   for( i = 0; i < numRandom; i++ )
   {
      r = rand() % RANGE;              // Changed to a random number between 0 and RANGE-1 inclusive (for convenience)
      x[i] = r;                        // Store the random number (assuming that you really want to)
      count[r]++;                      // Add to count for this value
   }


   cout << "\nThe original random numbers are:\n";
   for( i = 0; i < numRandom; i++ ) cout << x[i] << " ";


   cout << "\n\nThe random numbers in order are:\n";
   for ( j = 0; j < RANGE; j++ )
   {
      for ( i = 0; i < count[j]; i++ ) cout << j << " ";
      cout << endl;
   }


   cout << "\nThe random numbers by count are:\n";
   for ( j = 0; j < RANGE; j++ ) cout << j << ": " << count[j] << endl;
}