Generating random non repeating number array in C++

Question

I need to generate random non repeating number array in C++, in this part of code I generate random numbers using, srand function, but some of the numbers are repeating. The main task is to generate random numbers for lottery ticket, so I need to generate numbers until golden number which is marked as int golden.

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

using namespace std;

int main()
{
  int golden = 31;
  int i = 0;
  int array[35];

 srand((unsigned)time(0));
    while(i != golden){
        array[i] = (rand()%75)+1;
        cout << array[i] << endl;
        i++;
}
 }

Related: stackoverflow.com/questions/22842289 stackoverflow.com/questions/9755538 [python using built-in] stackoverflow.com/questions/14473321 stackoverflow.com/questions/196017 — user202729
– user202729, Commented Apr 11, 2018 at 8:24

NPE · Accepted Answer · 2014-09-16 20:53:07Z

7

One strategy is to populate an array with numbers from 1 to 75, and then use std::random_shuffle() on it. You can then read the numbers from the array until you hit the golden number.

answered Sep 16, 2014 at 20:53

NPE

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Comments

MildThrone · Accepted Answer · 2021-04-25 18:54:07Z

I had a similar task and used two functions to solve the problem of repeating numbers.

#include <iostream>
#include <ctime>

using namespace std;

void generateRandom(int array[], int length);
bool findVal(int array[], int size, int value);

int main() {
    int arraySize = 10;
    int array[arraySize];

    generateRandom(array, arraySize);
    for (auto i : array) {
        cout << i << " ";
    }

    return 0;
}

void generateRandom(int array[], int length) {
    srand((int) time(nullptr));
    int temp;

    for (int i = 0; i < length; ++i) {
        temp = rand() % 20 + 1;
        if (findVal(array, i, temp)) {
            i--;
            continue;
        } else {
            array[i] = temp;
        }
    }
}

bool findVal(int *array, int size, int value) {
    for (int i = 0; i < size; ++i) {
        if (array[i] == value) {
            return true;
        }
    }
    return false;
}

Within the generateRandom function, you can switch the 20 and 1 used in the for loop with your preferred upper and lower limits respectively.

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