Kth prime number greater than N in C++

In this tutorial, we are going to write a program that finds the k-th prime number which is greater than the given number n.

• Initialise the number n.
• Find all the prime numbers till 1e6?? and store it in a boolean array.
• Write a loop that iterates from n + 1 to 1e6?.
  • If the current number is prime, then decrement k.
  • If k is equal to zero, then return i.
• Return -1.

Example

Let's see the code.

 Live Demo

#include <bits/stdc++.h> using namespace std; const int MAX_SIZE = 1e6; bool prime[MAX_SIZE + 1]; void findAllPrimes() {    memset(prime, true, sizeof(prime));    for (int p = 2; p * p <= MAX_SIZE; p++) {       if (prime[p]) {          for (int i = p * p; i <= MAX_SIZE; i += p) {             prime[i] = false;          }       }    } } int findKthPrimeGreaterThanN(int n, int k) {    for (int i = n + 1; i < MAX_SIZE; i++) {       if (prime[i]) {          k--;       }       if (k == 0) {          return i;       }    }    return -1; } int main() {    findAllPrimes();    int n = 5, k = 23;    cout << findKthPrimeGreaterThanN(n, k) << endl;    return 0; }

Output

If you run the above code, then you will get the following result.

101

Conclusion

If you have any queries in the tutorial, mention them in the comment section.