Using Rand with range.

[kay19]

Hello, very new to C++. I have to initialize an Array of 5000 and use the Srand & Rand, where the range would be -8191 to 8192. Let me provide what I have done so far

#include <iostream> 
#include <cstdlib>
#include <time.h>  
using namespace std;

const int SIZE = 5000; 
void fill(int []);

int main (void) { 
          srand (time(0)); 
          int int_ary[SIZE]; 

        fill (int_ary);
        int test = int_ary[rand()% ((0 + 16383)-8191)];

        cout << "Element: " << test
        << " is located at index: " 
        << endl; 
        system("PAUSE");
 
 return 0; 
} 

void fill (int ary[]) { 
for (int k=0; k<SIZE; k++) { 
ary[k] = rand(); 
} 
}

So that's what I think how the range would work, but not sure based on my compiling. Any help is appreciated.

[1v5E3TCk]

rand()% ((0 + 16383)-8191) that wont give you a value between -8191 and 8192. It gives you a vlue between 0 and 8191. You have problem with brackets.

Try that:

(rand()%16383) - 8191

[Chervil]

I'm not sure what is your intention. Is it to fill the array with random values in the range of -8191 to 8192 ?

Your current code seems to generate array subscripts which are in the range 0 to 8191 which is a bit awkward, as the array contains only 5000 elements.

Generate random in a particular range:

int rnd(int from, int to)
{
    return from + rand() % (to - from + 1);
}

[kay19]

Thanks for the replies. Let me clarify a bit more what I have to do. "perform a search and display elements of an array. Initialize an integer array of 5,000 elements with random integers, using srand & rand functions in the range: -8192 to 8191 (duplicates permitted). Prompt the user to enter an integer to search (from the front of the array) & output the index location of the element found (negative 1 if not found)".

So starting out step by step by initializing an array, then using srand & rand for the range. Once I figured that out, i'll continue to do more coding.

[Chervil]

So your fill function should do something like this:

void fill (int ary[])
{ 
    const int from = -8192;
    const int to   = +8191;
    
    for (int k=0; k<SIZE; k++) 
    { 
        ary[k] = from + rand() % (to - from + 1); 
    } 
}

edit: The original post said: "where the range would be -8191 to 8192" while the newer post says: "-8192 to 8191"
I'll leave it for you to figure out which is required.

[1v5E3TCk]

I didnt really understand what you want to do :D but as I understood,

-you will initialize an array of 5000 elements which are generated by rand() in the range -8192 to 8191
-and you will ask a number to search and show the index of that number

is it right?

if it is right you can do it like that:

int main()
{
    int SIZE = 5000;
    int ary[SIZE];
    int search_for;
    int index = -1;

    const int from = -8192;
    const int to   = +8191;
    
    for (int k=0; k<SIZE; k++) 
    { 
        ary[k] = from + rand() % (to - from + 1); 
    } 

    cout << "Enter the index\n";
    cin    >> search_for;

    for(int i = 0; i<SIZE; ++i)
    {
         if( ary[ i ] == search_for )
         {
               inex = i;
         }
    }

    cout << index;
}

I hope it helps

EDIT: changed the code with Chervil's one

[kay19]

Appreciate the help people. Sorry about the range difference confusion. :P

EDIT: I think I understand the question of this program. It wants to produce an index of various numbers up to 5000. I.E [0] -945, [1] -47...[4999] 74.

Afterwards, i'll have to code in user input to search for a number.