Deleting from an array and shifting - c++

Question

For an array, say, size 5,
I'm trying to find a random position between 0 and the current last element of the array.
(This last position is 4 the first time, will be 3 the second time, and so on.)
Delete whatever element is in that array position, shifting all elements above it down so that there are no empty spots in the array.
I am trying to be as time-efficient as possible, so I want to avoid setting said random position to 0 or something like that.
So if my array looked something like int n[] = {1,3,5,7,9}; and my random position finder chose position 2, how would I move 5(position 2) to the end and shift everything down so that my resulting array looks like {1,3,7,9,5} ?
So far I have:
for (int j = 0; j < 5; j++)
{
printf ("before removal:\n");
printarray (array, 5);
int randompos = ( rand() % (5-j) ); //selects random number from 0 to active last pos.
/* ?????? */ = array[randompos]; // What position will hold my random position?
//Also, what goes in place of the 'deleted' element?
insertion_sort (array, 5-j); //sort only the active elements
printf ("after removal:\n");
printarray (array, 5);
}
desired output:
before removal:
1,3,5,7,9
(say random position was array position 2, storing number 5)
after removal:
1,3,7,9,5

Answer 1

Given the array {1,3,5,7,9} and pos = 2, you can do the following:
int main()
{
int pos = 2;
int arr[] = {1, 3, 5, 7,9};
int length =sizeof(arr)/sizeof(arr[0]);
int val = arr[pos];
for (int i = pos; i < length; i++){
int j = i + 1;
arr[i] = arr[j];
}
arr[length - 1] = val;
return 0;
}

Answer 2

#include <iostream>
#include <algorithm>
#include <random>
int main() {
int n[] = {1, 3, 5, 7, 9};
std::size_t n_size = sizeof(n) / sizeof(int);
std::default_random_engine generator;
for(std::size_t i(0), sz(n_size); i < sz; ++i) {
std::cout << "before removal:" << std::endl;
std::cout << " ";
for(std::size_t j(0); j < n_size; ++j) std::cout << n[j] << " ";
std::cout << std::endl;
--n_size;
std::uniform_int_distribution<int> distribution(0, n_size);
std::size_t idx = distribution(generator);
std::cout << " Removing index: " << idx << std::endl;
std::swap(n[idx], n[n_size]);
std::sort(std::begin(n), std::begin(n) + n_size); // use your sorting here
std::cout << "after removal:" << std::endl;
std::cout << " ";
for(std::size_t j(0); j < n_size; ++j) std::cout << n[j] << " ";
std::cout << "\n" << std::endl;
}
}
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