k'th largest element in an array

Question

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

using namespace std;

bool findNthMax(double arr[], int len, int n, double& nth_max)
{

sort(arr, arr+n);


//Counter
int c = 1;

//Initialize nth max
nth_max = arr[0];

//Loop in the array while the count is less than (n)
for (int i = 0; i < len && c < n; i++)
{

    if (arr[i] != nth_max)
        c++;


    nth_max = arr[i];

}

return nth_max;

}

int main()
{
int n;
double arr[10];
double y;

cout << "The random array elements are:" << endl;

srand((unsigned)time(0));
for(int i=0; i<10; i++){
    arr[i] = (rand()%100);

    cout << arr[i] << ' ' ;

}

cout << endl;
cout << "Input a positive integer n: " ;
cin  >>  n ;

if(n>10)
cout << "The nth largest value does not exist." << endl;
else
cout << "The nth largest value is: " << findNthMax(arr, 10, n, y) << endl;

return 0;

}

EDIT: the function returns false if the nth largest value does not exist; the first parameter is the input array; the second parameter is the array size; the third parameter is used to pass the value of n to the function; the last parameter is nth largest value being found.

The main function generates an array with 10 double random elements (in the range [0, 99]. It prints out those 10 elements. Prompt a user to enter a positive integer n, then print out the nth largest value in the array.

How ever my outputs shows that nth largest: 1 when n = 2

Answer 1

You're incrementing c to 2 after if arr[1] != nth_max . This means that c !< n , so you're for loop exits after 2 loops through.

You need to sort the entire array, b/c you're missing the case where you could have 8 duplicates before the 2nd max, for instance { 8, 8, 8, 8, 8, 8, 8, 8, 1, 2, 8, 8, 8 }.

sort(arr, arr+len);

You should start your for loop at the end of the array...

nth_max = arr[len-1];    
for (int i = len-1; i >= 0 && c < n; i--)

Then also run the function before outputting the variable y :

findNthMax(arr, 10, n, y);
cout << "The nth largest value is: " << y << endl;